Convert datadir pytest into CI tests

Convert test from #25 to CI tests using [integration test framework](https://github.com/dogecoin/docker/tree/main/tests/integration).
```python
def test_datadir(hook, host):
"""
Verify if datadir can be changed and created proprely.

Verify datadir metada, if it's owned by script user (dogecoin).
"""
# Use a unique directory for this test
tmp_datadir = "/tmp/datadir_test"
datadir_argument = f"-datadir={tmp_datadir}"

test_args = ["dogecoind", datadir_argument]
test_environ = {}

result_args = [
pytest.abs_path("dogecoind"),
datadir_argument,
"-printtoconsole",
]
result_environ = {}

# Run test to generate datadir
hook.test(test_args, test_environ, result_args, result_environ)
assert hook.result == hook.reference

# Test datadir metadata
datadir_folder = host.file(tmp_datadir)
assert datadir_folder.user == pytest.user
assert datadir_folder.group == pytest.user
assert datadir_folder.mode == 0o755
```