refactor: schema endorsement flow for shared and dedicated agents (BE)

[pranalidhanavade]

• [x] Refactor schema endorsement flow for shared and dedicated agents.
• [x] Testing of schema endorsement for INDY and W3C schema types with sign and sign and submit flow.
• [x] Testing of schema endorsement flow from API side for shared and dedicated agents with INDY, POLYGON, KEY and WEB. - Schema endorsement for shared agent to shared agent. - Schema endorsement for dedicated agent to dedicated agent. - Schema endorsement for shared agent to dedicated agent. - Schema endorsement for shared dedicated to shared agent.