Implement get_root_keys to the AdminKeyValueStore

[MathieuDutSik]

Motivation

We need to have the feature of accessing to the list of root keys in order to have mutation function and accessing to the list of chain ids of a storage.

Fixes #3085

Proposal

The implementation causes some problems:

• For ScyllaDb / DynamoDb the implementation is very easy since the root_key is used as a partition key.
• For RocksDb / StorageService / IndexedDb we need to keep track of the list of root_keys.
• The result of the get_root_keys will not be the same on different storage. If storage has been created with fn create but no key is inserted then in ScyllaDb / DynamoDb it will not show the root_key but in RocksDb it will appear.

The end result is that the fn connect becomes slower for RocksDb, StorageService, IndexedDb but this is I think fine as the issue of performance shows up in other operations.

Test Plan

One test has been added for this feature.

Release Plan

No impact on the TestNet / DevNet. It can follow the normal release plan.

Links

None.