governance/maintenance: add triage rotation workflow

[alexhancock]

Motivation and Context

• Set up a rotation for issue/PR triaging
• Round robins to the members of the rust-sdk-maintainers
• The expectation will be that the currently active member will make sure new Issues are triaged in two business days (when on rotation) and that critical PRs (P0/P1) are resolved within seven days

How Has This Been Tested?

• Will test as it merges & activates in GitHub actions for the repo
• First week or so will just be making sure it's set up correctly. I will handle initial triage.

Breaking Changes

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

N/A