DOCS: Add the changelog feature

[ecoussoux-ansys]

This PR is implementing the ansys/actions/doc-changelog in .github/workflows/label.yml and the ansys/actions/doc-deploy-changelog in .github/workflows/ci_cd.yml.
Combined, these actions will automatically generate a changelog section inside the pyedb documentation, making it easier for users to get an overview about the chronology of the latest changes.
The two ansys/actions are added following the documentation provided here and here.

For each merged PR, a changelog fragment will now be produced and stored in the doc/changelog.d folder. Upon each new release, these fragments will be assembled to form the release notes that will be added to the documentation in the doc/source/changelog.rst file. Once this operation is performed, the combined fragments will be automatically deleted.
The tool used for the generation of the changelog fragments and release notes is towncrier.
A link to the changelog inside the documentation is also introduced in the doc/source/index.rst file.

[ecoussoux-ansys]

@SMoraisAnsys, tagging you here essentially to make sure that the pyansys-ci-bot is granted the necessary rights in the repository to run the actions. Thanks!

[ecoussoux-ansys]

@svandenb-dev, I noticed that the doc/source/changelog.rst file already existed in pyedb (apparently introduced in #1468), but it seems that it was not really maintained.. it contained only elements related to a release that is more than 1 year old.. The idea with the new actions introduced here is to have the release notes automatically added to that file for every new release going forward.
So what do you think we should do with that older content? Keep it (with maybe some minor additions mentioning that the content is "pre v0.62.0") and simply let the newly introduced actions write the changelogs for the releases to come at the top of the file? Or delete these older entries and start again with a "fresh" changelog?
@SMoraisAnsys, I'd be interested to hear your thoughts on that too, if you have any.
Thanks!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.96%. Comparing base (67790a3) to head (e75aee8).

Additional details and impacted files

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  Files         267      267           
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  Misses      11930    11930           

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[svandenb-dev]

LGTM

[SMoraisAnsys]

LGTM