Add Namespace functions for rocksdb interaction

[SimranMakhija7]

The namespace file in the repository module implements the following functionalities:

1. list all namespaces
2. Create a namespace, with an optional set of properties. The server might also add properties, such as last_modified_time
3. Load the metadata properties for a namespace given its name
4. Check if a namespace exists
5. Delete a namespace given its name
6. Set and/or remove properties on a namespace.