Enables stale bot to automatically closed old issues in this repo.
https://github.com/actions/stale

This action is largely based on a reusable workflow from Mu DevOps.

Current configuration:
  - Stale PR: After 60 days
  - Stale Issue: After 45 days
  - Days until PR and Issue close: 7 days
  - Exempt labels:
    - `impact: security`
    - `security` - `stale: ignore`
  - Stale Issue label: `stale: issue`
  - Stale PR label: `stale: pr`
  - Comments are left when marked stale and when closed

These settings come directly from the default setting values in
the Mu DevOps reusable workflow.

Note: The `workflow_dispatch` trigger is added to allow the workflow to be manually
invoked if ever needed.

- [ ] Breaking change?
  - Will this change break pre-existing builds or functionality without action being taken?
  **No**

Verified workflow on mu_basecore fork.

Example run: https://github.com/makubacki/mu_basecore/actions/runs/3526648651

N/A - Only affects the GitHub workflow in this repo

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>