[Epic] V4 API cleanup

[andrewazores]

Describe the feature

See also #66 - these API/model improvements should also be included as a Step 0.

1. ([Story] API V4 paths and formats cleanup #583) Remove API endpoints that simply redirect clients to newer API versioned endpoints. Redirects for other purposes will remain, ex. redirecting for file downloads
2. ([Story] API V4 paths and formats cleanup #583) Remove v2.x API response formatting and return to simpler JSON response structures everywhere applicable
3. ([Story] API V4 paths and formats cleanup #583) Rename remaining API endpoints to V4
4. [Request] Long-running API operations should return Accepted response and notify by WebSocket #286
5. Update Agent to use V4 endpoints
6. Update web-client to use V4 endpoints

Anything other information?

No response