feat: changelog action & example

[klmcadams]

The changelog action uses towncrier and adds fragments (files) to a directory of your choice based on your pyproject.toml settings for towncrier. Each fragment is named in the format pr_number.pr_label.md. The pr_label is determined by the labels in the pull request. For example, if you have the "enhancement" and "maintenance" labels, it will set the pr_label as "added". This means the fragment will be added to the changelog under the "Added" subsection. Side note - it seems like the majority of PRs have the maintenance label, so that's why I chose to categorize the PR based on other labels other than maintenance.

I think it would make the most sense to put this action at the end of the .github/workflows/label.yml file. For this action to work, you have to add the "types" line under "pull_request:" in label.yml file:

on:
  pull_request:
    # opened, reopened, and synchronize are default for pull_request
    # edited - when PR title or body is changed
    # labeled - when labels are added to PR
    types: [opened, reopened, synchronize, edited, labeled]

labeler:
...

changelog-fragment:
  name: "Create changelog fragment"
  needs: [labeler]
  runs-on: ubuntu-latest
  steps:
    - uses: ansys/actions/doc-changelog@{{ version }}
      with:
        token: ${{ '{{ secrets.GITHUB_TOKEN }}' }}

Here is an example of how to set up your repository to use towncrier/this action: https://github.com/ansys/ansys-templates/compare/demo/changelog-action?expand=1

This action will only create the fragments for the changelog. You will have to run towncrier build --yes --version <version> to create the changelog using these fragments. Here is an example: https://towncrier.readthedocs.io/en/stable/markdown.html

This PR is the same as #357 but has less commits so it would be easier to review. I figured I could go over this with everyone at the team meeting to get everyone's opinions :)

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[RobPasMue]

This is great @klmcadams! I will try to review it today

[RobPasMue]

Just curious - why did we close #357? Commits get squashed and merged anyway.

[RobPasMue]

Apart from my comments - looks amazing

[RobPasMue]

@klmcadams - could you add to docs/source/migration_guide.rst this new feature? (not as a breaking change - just new feature)

Explain as well in migration steps the changes needed to make it work.

[klmcadams]

Just curious - why did we close #357? Commits get squashed and merged anyway.

I closed it because there were a ton of comments and commits, so I thought it would be easier to review if I started a new PR

[RobPasMue]

We have to discuss the location of all these steps. I don't believe it's a migration guide because it is not a breaking change, but a new feature.

PS.: I know I said "add it to the migration steps guide" in my initial comment, the content is great in any case, let's just discuss where to put it =)