refactor(config): enable default environment token per hvcs

[codejedi365]

Purpose

Update the configuration parser to optionally default to the VCS specific token

Rationale

In preparation to facilitate the request of #734, I need to find a way to solve the missing token when the remote.type is none. This led me to determining that it would be helpful if we looked for the default token names for each of the VCS. This refactor enables the configuration to be aware of each VCS's default.

Current downside is that Gitea does not provide a pre-authed CI-like token based on this discussion. I just guessed to use GITEA_TOKEN. I could potentially have it be empty instead, which would force the user to provide it.

Consideration also should be made for GitLab as GitLab's default token CI_JOB_TOKEN has permissions problems with python-semantic-release. The fact that python-semantic-release uses git push both commits and tags are both unauthorized actions by a CI_JOB_TOKEN. This means users are forced to provide a PAT as that is how we mark versions. What the users define as that token name is up to them. My guess would be to use GITLAB_TOKEN but maybe we need to force them to be specific here also. Curious on your thoughts.

Separately, there is still some investigation that I'm doing here to hopefully find a better implementation for GitLab.

One of the other issues (besides for none) that I have with the current implementation is that if the user does not know to specify a token value or forgets, we default to GH_TOKEN when I have specified remote.type = 'gitlab'.

How I tested

Build a paramaterized unit test with all the expected valid & invalid tests.

How to verify

git fetch origin pull/774/head:pr-774

# checkout the PR as a detached HEAD state with only the unit tests
git checkout pr-774~1 --detach

# execute tests, 2 should fail (non-github)
pytest tests/unit/semantic_release/cli/test_config.py

# update to the HEAD of the PR (with fixes)
git merge --ff-only pr-774

# run pytest again to see success
pytest tests/unit/semantic_release/cli/test_config.py

[bernardcooke53]

Looks solid, just a couple of minor comments - thanks @codejedi365 🚀

[bernardcooke53]

Thanks @codejedi365! 🚀