GD-Storage: Implement ConfigCache, Mutation, and MutationEntry

* ConfigCache: A quick and thread-safe container for in-memory configs
* Mutation and MutationEntry: Transaction based methods to make multiple
  modifications to ConfigCache atomically

Bug: 157533831
Bug: 157533958
Test: atest bluetooth_test_gd
Tag: #gd-refactor
Change-Id: I550b34071ed96147a4a044a8cee766aab866ae66