feat: vale ignore towncrier directory

[klmcadams]

Gives the option to ignore md files in the towncrier fragment file directory (typically doc/changelog.d). @da1910 ran into this issue where vale flagged codecov in the fragment file as an error. By default, the action will check the towncrier directory unless ignore-changelogd is specified.

If it makes more sense to ignore the changelog.d directory by default, then we can make the default value true. Let me know what you all think.

changelog.d directory not ignored: https://github.com/ansys/openapi-common/actions/runs/8930323884/job/24530231218?pr=575

changelog.d directory ignored & other rst files in doc are not ignored: https://github.com/ansys/openapi-common/actions/runs/8930356819/job/24530286024?pr=575

Closes #477

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[SMoraisAnsys]

I would go for ignoring by default. I assume that many people will end up facing this issue at some point and have to ignore the changelogd directory anyway.

[da1910]

Fix looks OK to me, I have no strong feelings about default/not, but the implementation looks reasonable (given my comments before about storing python in workflows)

[MaxJPRey]

I would go for ignoring by default. I assume that many people will end up facing this issue at some point and have to ignore the changelogd directory anyway.

I would also suggest to ignore it by default.