Add small fix and test to assert prepare_host hook is called with correct dirs

[whummer]

Add small fix and test to assert that prepare_host hooks are called with appropriate LocalStack directories layout. This is a follow-up from #8384 .

The previous PR #8384 adjusted the logic to start up LocalStack using the CLI when running inside a Docker container, for example to run localstack start in a Github Codespaces environment. This works well for the Community version, but unfortunately there was an oversight for the Pro version, where we're performing operations on the host via prepare_host hooks. In particular, the hook used to cache the key locally was failing with a PermissionError, as it was trying to access the wrong directory (using the container dirs layout, not the host dirs layout).

Traceback (most recent call last):
  File "/usr/local/python/3.10.4/lib/python3.10/site-packages/localstack_ext/bootstrap/licensing.py", line 64, in fetch_key
    C=json.loads(to_str(B.content))[_C];cache_key_locally(A,C)
  File "/usr/local/python/3.10.4/lib/python3.10/site-packages/localstack_ext/bootstrap/licensing.py", line 75, in cache_key_locally
    A=to_str(base64.b64encode(to_bytes(C)));E=get_key_cache();E.update({_E:int(B),_G:md5(api_key),_C:A});E.save()
  File "/usr/local/python/3.10.4/lib/python3.10/site-packages/localstack/utils/json.py", line 84, in save
    os.makedirs(os.path.dirname(self.path), exist_ok=True)
  File "/usr/local/python/3.10.4/lib/python3.10/os.py", line 215, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "/usr/local/python/3.10.4/lib/python3.10/os.py", line 225, in makedirs
    mkdir(name, mode)
PermissionError: [Errno 13] Permission denied: '/var/lib/localstack'

This PR contains a small follow-up change in cmd_start(..) to ensure bootstrap.prepare_host(..) is called after we're performing the config.* adjustments introduced in #8384 . The change has been tested in Github Codespaces, which now allows to spin up a Pro container via the CLI if the API key is configured. A unit test is added to cover the functionality, with assertions about the "is in Docker" status and the accessibility of the dirs.cache directory.

Note: The PR also contains a few minor cleanups/refactorings (add type hints, f-strings, etc) along the way.

[whummer]

This is effectively the main change in the PR - calling the hooks after we've adjusted the config values above.

[whummer]

nit: removed unused variable (duplicate from line 295 above, and not used further below)

[whummer]

security: changing to the non-shell subprocess execution here, to prevent potential command injection.

[coveralls]

coverage: 82.647% (-0.007%) from 82.654% when pulling a03fc9b on prepare-host-dirs into bee5f76 on master.

[github-actions]

LocalStack Community integration with Pro

       2 files         2 suites   1h 36m 25s ⏱️
2 166 tests 1 830 ✔️ 336 💤 0 ❌
2 167 runs  1 830 ✔️ 337 💤 0 ❌

Results for commit a03fc9b.

[thrau]

nice catch. changes make sense to me!