Zoekt: Add endpoint to support POST task requests

What does this MR do and why?

Our URL to the tasks API is very long, and we plan to add more parameters in the near future. For example, schema_version. In this MR adding a new POST heartbeat endpoint keeping the GET tasks endpoint for backward compatibility.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Checkout to the MR branch
• Make sure all the migrations are executed

bin/rails db:migrate

• Run the zoekt indexer from this branch gitlab-zoekt-indexer!462 (merged)
• Verify in the log/development.log you are getting the request to the heartbeat endpoint
• Snippet from the log POST /api/:version/internal/search/zoekt/:uuid/heartbeat

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #537000 (closed)