[azure] Adding new API to create public schemas in azure

Changes in the MR:

1. A new azure only API named /system/schema Find details here: #51
2. The API works with service principal authorization only
3. All the classes interacting with cosmosStore and blobStore have this intelligence added to identify whether any schema has to be created in system related cosmos/ blob or tenant specific cosmos/ blob. This identification is done using the data-partition-id header.
4. The older way of creating public schemas is still supported.
5. The new API sets data-partition-id as shared.tenant.name to induce the public schema scenraio.
6. Both entry points to create public schemas converge at provider/schema-azure level, hence all the public schemas would be created at system resources only. Even the older API is passing common as data-partition-id, in reality there is no common tenant; as far as public schemas are concerned.