Refactor SchemaRepositoryProvider into its own component

As noted in NETCONF-671, we have had duplicate implementations of this interface. Further examination reveals this is actually left completely unused, and only the static factory is used instead.

That static factory has further problems:

• requires static wiring
• contains duplicate code (AbstractTopology vs. NetconfTopologyUtils)
• all lifecycle around multiple directories is non-existent due to it being tracked in a static map only
• there is no way to provide customized implementations

Hence this issue is about factoring the static mess out into something that has clear lifecycle and is injected into topology instances.