Auto-generate preview links for DOC PRs

[debadair]

Adds a GitHub Action that will automatically create preview links when a doc pull request is created. Links are added in a comment on the PR.

Borrowed from @richkuz -- Thanks!

[elasticsearchmachine]

Pinging @elastic/es-docs (Team:Docs)

[bmorelli25]

You might consider adding a path filter so that a comment is only added to PRs that change docs.

I haven't done this myself, but it might look something like this:

on:
  pull_request_target:
    types: [opened]
    paths:
      - 'docs/*'
      - 'add_other_doc_dirs_here'

Or even better, target asciidoc files: - '**.asciidoc'.

on:
  pull_request_target:
    types: [opened]
    paths:
      - '**.asciidoc'

I think. Again, I haven't tested this.

[debadair]

Ah, yes, good point! Targeting asciidoc files seems like the ticket.

[richkuz]

LGTM @debadair 👍

[bmorelli25]

🚢

[bmorelli25]

Excited to see this in action!