Add ServiceExpiredCallback

This is a no-op change and refactors the design for subsequent
TTL expiration check changes.
- Add a ServiceExpiredCallback to notify expired services.
- To simplify the design, pass the CacheKey to MdnsServiceCache
  methods instead.

Bug: 265787401
Test: atest FrameworksNetTests CtsNetTestCases
Change-Id: I930a4f7baf9b8d3d0037dc6aefd717dbdd486520