Add script to run Vale linting on PRs

[gaurav-nelson]

This adds a bit relaxed version of Vale linting for PRs. For https://issues.redhat.com/browse/TELCODOCS-1327

• It would only check if modified lines have any error and would add a comment to the PR. The check would always pass and won't stop people from merging PRs in case of false positives.
• Only lists issues of type error and not warning and info.
• Only checks for updated AsciiDoc and Markdown files under the following directories:
  • content/learn/*
  • content/patterns/*
  • content/contribute/*
  • modules/*

Sample comment would be similar to the following:

📝 Vale Linting Results

Vale found 3 issue(s) in the modified lines of this PR.

content/patterns/ansible-edge-gitops/cluster-sizing.adoc

• Line 14: Keep one space between words in 'metal. For'. [RedHat.Spacing] (error)

content/patterns/ansible-edge-gitops/getting-started.adoc

• Line 261: Use 'Mozilla Firefox' rather than 'Firefox'. [RedHat.TermsErrors] (error)
• Line 319: Use 'Mozilla Firefox' rather than 'Firefox'. [RedHat.TermsErrors] (error)

---

This comment was automatically generated by Vale on the modified lines.

This PR is part 2 of the change. I still need to add configuration and updates to the OpenShift CI. Please see the Jira issue for more details.

[ocpdocs-previewbot]

🤖 Thu Sep 18 00:52:52 - The preview is ready at:
https://604--patternsdocs-pr.netlify.app

[mhjacks]

LGTM