Experimental/rocks db support

[sergiy-skalelabs]

• Added Rocks DB support
• Added Memory DB support
• Added --db=*** command line argument to specify values like rocksdb / leveldb / memorydb, default is leveldb for backward compatibility
• Rocks DB is used everywhere in skaled if --db=rocksdb command line argument specified
• SKALE-specific class MemoryDB renamed to MemoryDB_S, because new MemoryDB class is working memory database backend now
• SplitDB class commented/removed because it's not used
• DBImp.h file and namespace DBImp were removed because they are no longer needed
• Added/restored DBFactory class and it's used everywhere in skaled to create DB instants of backed type specified by --db=***`

[github-actions]

SUGGESTIONS BEFORE MERGE:

1. Build custom container here: https://github.com/skalenetwork/skaled/actions?query=workflow%3A%22Custom+Docker+and+Binary%22
2. Test it here: https://github.com/skalenetwork/skale-ci-integration_tests/actions?query=workflow%3A%22Skaled+Nightly+Tests%22
3. Edit VERSION file appropriately to your changes!
   See https://skalelabs.atlassian.net/wiki/spaces/SKALE/pages/2444951553/Branching+instructions