Draft: Add capitalization rule to vale

What does this MR do?

After and internal discussion, we realized we were using markdownlint (a Markdown formatting linter) to lint for language issues, which we normally reserve for Vale (a language linter).

This MR:

• Removes the MD044 rule from the markdownlint configuration, greatly simplifying the file. I don't think we were maintaining the list very actively anyways.
• Adds the capitalization entries to a new Vale vocabulary: https://vale.sh/docs/topics/vocab/
• Removes the markdownlint lint exceptions for MD044, and replaces them with an equivalent Vale exception.
  • Note that the Vale exception was not needed in many places, Vale was happy to ignore things that were false positives for markdownlint.

Related issues

• Related to Convert the GitLab Vale styles directory `gitla... (technical-writing#1209)
• Related to https://gitlab.com/gitlab-org/gitlab/-/issues/47389+

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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