`blenderproc.command_line:cli` in entrypoints but not importable / side effects in __init__.py

### Describe the issue

The setup.py file [specifies](https://github.com/DLR-RM/BlenderProc/blob/3b4c4e4da069798cce36f419da79369fc72a73cb/setup.py#L21) `blenderproc.command_line:cli` as an "entry point", which [implies](https://packaging.python.org/en/latest/specifications/entry-points/#use-for-scripts) that it should be possible to import the `blenderproc.command_line` module and call its `cli` function like so:

```python
import sys
from blenderproc.command_line import cli
sys.exit(cli())
```

This ends up importing [`blenderproc`](https://github.com/DLR-RM/BlenderProc/blob/3b4c4e4da069798cce36f419da79369fc72a73cb/blenderproc/__init__.py#L57-L62) too and currently fails with:

```bash
❯ python
Python 3.10.12 (main, Jun 6 2023, 22:43:10) [GCC 12.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from blenderproc.command_line import cli
Traceback (most recent call last):
File "", line 1, in
File "/nix/store/g0clcimnb9pmlil358yw176x3c57m4ph-python3-3.10.12-env/lib/python3.10/site-packages/blenderproc/__init__.py", line 60, in
raise RuntimeError("\n###############\nThis script can only be run by \"blenderproc run\", instead of calling:"
RuntimeError:
###############
This script can only be run by "blenderproc run", instead of calling:
python
call:
blenderproc run
###############
>>>
```

Another reproducer:

```bash
❯ python
>>> import importlib.metadata
>>> importlib.metadata.EntryPoint("blenderproc", value="blenderproc.command_line:cli", group="console_scripts").load()
Traceback (most recent call last):
File "", line 1, in
File "/nix/store/lx8vhp4fxclp494svlfis3sb2g8z4l9h-python3-3.10.12/lib/python3.10/importlib/metadata/__init__.py", line 171, in load
module = import_module(match.group('module'))
File "/nix/store/lx8vhp4fxclp494svlfis3sb2g8z4l9h-python3-3.10.12/lib/python3.10/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "", line 1050, in _gcd_import
File "", line 1027, in _find_and_load
File "", line 992, in _find_and_load_unlocked
File "", line 241, in _call_with_frames_removed
File "", line 1050, in _gcd_import
File "", line 1027, in _find_and_load
File "", line 1006, in _find_and_load_unlocked
File "", line 688, in _load_unlocked
File "", line 883, in exec_module
File "", line 241, in _call_with_frames_removed
File "/nix/store/g0clcimnb9pmlil358yw176x3c57m4ph-python3-3.10.12-env/lib/python3.10/site-packages/blenderproc/__init__.py", line 60, in
raise RuntimeError("\n###############\nThis script can only be run by \"blenderproc run\", instead of calling:"
RuntimeError:
###############
This script can only be run by "blenderproc run", instead of calling:
python
call:
blenderproc run
###############
```

It would resolve the issue, for example if all the side effects such as `raise` and `pip install`, weren't unconditionally invoked at import time, but rather were moved to a function that the user (and the `cli()`) would call explicitly. In addition, this would simplify packaging blenderproc in distributions other than PyPi

Thanks!

### Minimal code example

_No response_

### Files required to run the code

_No response_

### Expected behavior

Blenderproc CLI synopsis printed

### BlenderProc version

v2.6.1

### Related

- https://github.com/DLR-RM/BlenderProc/issues/901
- https://github.com/DLR-RM/BlenderProc/issues/840

...are related, except the present issue is more narrowly-scoped

Start with the entry point in setup.py and the import-time behavior in blenderproc/__init__.py. Run the reported `from blenderproc.command_line import cli` reproducer and inspect how the command_line entry point loads. Done means the module imports without the current RuntimeError or other import-time side effects, and the CLI synopsis is printed as expected.

Written by the indexing model from the issue text.