Centralized cache manager

FireFly has lots of isolated usage of `ccache` in many different managers. See [here](https://github.com/hyperledger/firefly/blob/bd63308c8cc855b4859ffc114d4ef6fcdcd7f42e/internal/identity/identitymanager.go#L66) and [here](https://github.com/hyperledger/firefly/blob/bd63308c8cc855b4859ffc114d4ef6fcdcd7f42e/internal/blockchain/ethereum/ethereum.go#L68) for examples.

It would make sense to consolidate this under a new, centralized Cache Manager component. It should be created under `internal/cache` and should follow the pattern set by other managers, particularly the Metrics Manager. It should be a singleton like Metrics Manager, and should be initialized early by Namespace Manager (the root manager). It can then be passed to all other plugins and managers that require it.

The interface can be quite simple, likely something like `Get(category string, key string)` and `Set(category string, key string)`.

As part of this, it would also make sense to consolidate the config options under a top-level `cache` key. The blockchain cache is already [following this pattern](https://github.com/hyperledger/firefly/blob/bd63308c8cc855b4859ffc114d4ef6fcdcd7f42e/internal/coreconfig/coreconfig.go#L124), but other cache configuration is scattered at various levels throughout the config tree. The old keys should be deprecated in favor of new ones that are grouped together under `cache`.