Refine ansibot actions on documentation issues and PRs

[acozine]

We have 3 labels on the ansible/ansible repo related to documentation: docs, docsite, and docsite_pr. To make it easier to find relevant issues, we'd like to define and refine the way Ansibot uses these labels.

• Ansibot should add docs to all issues PRs related to documentation (including module docs and anything in the docs/directory)
• Ansibot should add docsite_pr to all PRs that come from the "Edit on GitHub" feature with the label docsite_pr - all docsite_pr PRs should also get the docs label
• Ansibot should not assign the label docsite - we would like to reserve this for issues and PRs related to UI/UX improvements for the documentation, and we'd like to add it manually

Current behavior seems inconsistent, or maybe it has just changed recently. Here are some current issues/PRs to demonstrate what Ansibot currently does with the 3 docs-related labels:

ansible/ansible#55935
ansible/ansible#52605
ansible/ansible#50197

Once the bot behavior is firmed up, we'll document the rules here: https://docs.ansible.com/ansible/devel/community/documentation_contributions.html#community-documentation-contributions

[acozine]

Related to ansible/community#389.