Monovertex changes to support serving as a builtin source

[yhl25]

Some changes to the user facing APIs also will be made in this PR:

• POST /v1/process/sync - Receive payload and return result synchronously. If client gets disconnects (network error or timeouts), the results can still be retrieved using /v1/process/serve endpoint
• POST /v1/process/async - Receive payload and process asynchronously.
• GET /v1/process/serve - Receive processing status and/or results. The request may be submitted using /sync or /async endpoint.
• GET /v1/process/message - Retrive message graph for a request id

When submitting the request (either /sync or /async), the request id must not already exist in the store (for the duration of the store TTL). This is needed to avoid accidental overwrite of the results. A query parameter can be provided to allow overwriting.

The callback info will be saved in memory. It will be saved to Redis when the pod is shutting down or when all callbacks for a request id is received.