maint: Add stale github action

[MikeGoldsmith]

Description

Adds a GitHub Action to automatically mark stale PRs and close them after inactivity, adapted from the opentelemetry-java workflow.

• PRs with no activity for 14 days are marked stale by
  • by adding a stale comment from configuration
  • adding the "Stale" label
• Stale PRs with no activity for a further 7 days are closed
• Issues are not affected

Type of change

• 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 not work as expected)
• This change requires a documentation update

How Has This Been Tested?

CI-only change, no code tests applicable.

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated