Add a new SchemeShard type for system views and appropriate scheme operations

[n00bcracker]

To store ACL of sys views in SchemeShard we have to create sys view paths during init stage of SchemeShard.
We decided to use a new dedicated type for sys views objects.
To support a new type in SchemeShard we have to make changes:

• Store sys view path info in local DB
• Load sys view path info from local DB during init stage
• Store temporary sys view path changes in memory
• Add two new scheme ops: Create sys view and drop sys view
• Each sys view is determined by its type (implementation in KQP)
• Support sys view path description
• Write ut tests for a new sys view SchemeShard type