drpc,server: auto-generate HTTP routes for mux registration

[shubhamdhama]

Tracking this #152016 (comment) as an issue.

The original plan (#151396 (comment)) was to manually register endpoints and handlers for our API. This involved adding infra code to execute RPCs, write responses in JSON, and handle errors. The new approach is to use existing API infrastructure and automates the creation of routes, which was previously a manual step.

Jira issue: CRDB-54172