Docs: Update to use yaml file

[CamStan]

Description

Read the Docs has moved to a yaml file format that is needed to continue building our docs in the future. This adds that file.

This enables fail_on_warning to check for rst syntax errors when building. Builds for pull requests has also been enabled to add a status check to open pull requests. PR builds will be skipped if there are no changes to the docs. These features can easily be disabled if they don't work as desired.

Motivation and Context

Read the Docs will stop building any documentation not using this format in the near future.

How Has This Been Tested?

Docs were build in a test repo.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Testing (addition of new tests or update to current tests)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the UnifyFS code style requirements.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted.