feat: implement multi-did creation and management (default DID) for an organization (BE)

[tipusinghaw]

trafficstars

• [x] Create table mapping with org_agents and DID and the user can able to set the flag to primary-did
• [x] Create an API to fetch the org_agent's DID list
• [x] Update the create DID API for the default DID scenario
• [x] Create an API to set the default DID

[tipusinghaw]

This is completed