Make service reasons symbols, make http layer interpret them to status codes

Why

During some of the snippet refactors to comply with rubocop, we have updated some of the services to use the name arg :reason but left some services still returning http status codes from that.

What

We want to return symbol reasons and let any http layer callers interpret that into status codes on their own.

Implementation plan

You can use this MR and discussion !184082 (comment 2394050646) as inspiration. But in short:

• return symbols from service reasons
• have http layer interpret that as needed into http status codes
• see if any other callers are impacted