Some plugins can't run because they can't be "installed" first.

# Observed Issue

After following instruction from readme, FACT does run but some analysis plugins don't because they require docker images that can't be pulled. For instance, `file_system_metadata` fails with the following error:

```
[2023-09-25 13:26:16][docker][WARNING]: [file_system_metadata]: encountered docker error while processing
Process ExceptionSafeProcess-22:8:
Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/docker/api/client.py", line 268, in _raise_for_status
response.raise_for_status()
File "/usr/local/lib/python3.8/dist-packages/requests/models.py", line 960, in raise_for_status
raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found for url: http+docker://localhost/v1.43/containers/create
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/docker/models/containers.py", line 819, in run
container = self.create(image=image, command=command,
File "/usr/local/lib/python3.8/dist-packages/docker/models/containers.py", line 878, in create
resp = self.client.api.create_container(**create_kwargs)
File "/usr/local/lib/python3.8/dist-packages/docker/api/container.py", line 428, in create_container
return self.create_container_from_config(config, name)
File "/usr/local/lib/python3.8/dist-packages/docker/api/container.py", line 439, in create_container_from_config
return self._result(res, True)
File "/usr/local/lib/python3.8/dist-packages/docker/api/client.py", line 274, in _result
self._raise_for_status(response)
File "/usr/local/lib/python3.8/dist-packages/docker/api/client.py", line 270, in _raise_for_status
raise create_api_error_from_http_exception(e)
File "/usr/local/lib/python3.8/dist-packages/docker/errors.py", line 31, in create_api_error_from_http_exception
raise cls(e, response=response, explanation=explanation)
docker.errors.ImageNotFound: 404 Client Error for http+docker://localhost/v1.43/containers/create: Not Found ("No such image: fact/fs_metadata:latest")
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/docker/api/client.py", line 268, in _raise_for_status
response.raise_for_status()
File "/usr/local/lib/python3.8/dist-packages/requests/models.py", line 960, in raise_for_status
raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found for url: http+docker://localhost/v1.43/images/create?tag=latest&fromImage=fact%2Ffs_metadata
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3.8/multiprocessing/process.py", line 315, in _bootstrap
self.run()
File "/opt/FACT_core/src/helperFunctions/process.py", line 56, in run
raise exception
File "/opt/FACT_core/src/helperFunctions/process.py", line 51, in run
Process.run(self)
File "/usr/lib/python3.8/multiprocessing/process.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "/opt/FACT_core/src/analysis/PluginBase.py", line 140, in process_next_object
finished_task = self.analyze_file(task)
File "/opt/FACT_core/src/analysis/PluginBase.py", line 87, in analyze_file
fo = self.process_object(file_object)
File "/opt/FACT_core/src/plugins/analysis/file_system_metadata/code/file_system_metadata.py", line 65, in process_object
self._extract_metadata(file_object)
File "/opt/FACT_core/src/plugins/analysis/file_system_metadata/code/file_system_metadata.py", line 93, in _extract_metadata
self._extract_metadata_from_file_system(file_object)
File "/opt/FACT_core/src/plugins/analysis/file_system_metadata/code/file_system_metadata.py", line 104, in _extract_metadata_from_file_system
output = self._mount_in_docker(tmp_dir)
File "/opt/FACT_core/src/plugins/analysis/file_system_metadata/code/file_system_metadata.py", line 114, in _mount_in_docker
result = run_docker_container(
File "/opt/FACT_core/src/helperFunctions/docker.py", line 35, in run_docker_container
container = client.containers.run(image, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/docker/models/containers.py", line 822, in run
self.client.images.pull(image, platform=platform)
File "/usr/local/lib/python3.8/dist-packages/docker/models/images.py", line 444, in pull
pull_log = self.client.api.pull(
File "/usr/local/lib/python3.8/dist-packages/docker/api/image.py", line 428, in pull
self._raise_for_status(response)
File "/usr/local/lib/python3.8/dist-packages/docker/api/client.py", line 270, in _raise_for_status
raise create_api_error_from_http_exception(e)
File "/usr/local/lib/python3.8/dist-packages/docker/errors.py", line 31, in create_api_error_from_http_exception
raise cls(e, response=response, explanation=explanation)
docker.errors.ImageNotFound: 404 Client Error for http+docker://localhost/v1.43/images/create?tag=latest&fromImage=fact%2Ffs_metadata: Not Found ("pull access denied for fact/fs_metadata, repository does not exist or may require 'docker login': denied: requested access to the resource is denied")
[2023-09-25 13:26:16][PluginBase][ERROR]: Worker 0: Exception during analysis file_system_metadata on 0bd402cc5ef97c260e7b1486da0f841b84ffe8c0867dd48e08083b8f6d2e1806_21528576
```

# Identified Cause

Plugins never get a chance to be _installed_ by `start.py pull`. So for the above plugin example, the required local `fact/fs_metadata` docker image is never built by the plugin code as it should.

This happens because `distribution_check(allow_unsupported=False)` is called for any plugin installer being instantiated. `distribution_check` then calls `sys.exit(1)` because `fact-core-script` docker image is based on the "unsupported" Alpine.

## In details
(code snippets below are from `fact-core-script` image):

- `start.py pull` on the host runs `/opt/FACT_core/src/install.py --backend-docker-images --frontend-docker-images` in fact-core-script container.
- In `install.py`, method `install()` has the following :
```python
only_docker = not skip_docker and none_chosen and (args.backend_docker_images or args.frontend_docker_images)

# When just pulling the docker images we don't depend on anything distribution specific
distribution = check_distribution(allow_unsupported=only_docker)
```
- Here, `skip_docker=False`, `none_chosen=True`, and both checked `args.xyz` are `True` as well.
- Therefore, `check_distribution` emits warnings about the unsupported distribution (because the script docker image uses an "unsupported" Alpine), that we can ignore (as mentioned in issue #24 among others)
- Further down it calls `install_docker_images()` which in turns call
- `backend_install_docker_images()`: runs fine
- `backend_install_plugin_docker_images()`: fails!
- The latter call, at some point: `_install_plugins()` in `install/backend.py` with
```python
_install_plugins(distribution=None, skip_docker=False, only_docker=True)
```
- This finally calls `install_docker_images()` for each plugin found in the `plugins` folder.

Now, in the above example, with `file_system_metadata` plugin, there is:

```python
class FileSystemMetadataInstaller(AbstractPluginInstaller):
base_path = Path(__file__).resolve().parent

def install_docker_images(self):
self._build_docker_image('fact/fs_metadata:latest')
```

The base class `AbstractPluginInstaller` is initialized with:
```python
def __init__(self, distribution: Optional[str] = None, skip_docker: bool = skip_docker_env):
self.distribution = distribution or check_distribution()
self.build_path = self.base_path / 'build'
self.skip_docker = skip_docker
```

Here `distribution=None` so `check_distribution()` is called with default parameters, that is `check_distribution(allow_unsupported=False)`

Then the distribution check fails with
```python
logging.critical(msg)
sys.exit(1)
```

This obviously occurs on the first plugin installer that is instantiated, and the whole installation aborts at that point.

While a human could ignore "unsupported distribution" warnings as mentioned in #24 , the installer does not, and aborts. It does not seem to be the "intended behavior" as some plugins can't run if they are not previously installed from the above.