Secret Not Found - Inconsistent error codes

[XavierGeerinck]

URL of the docs page

https://docs.dapr.io/reference/api/secrets_api/#http-response

How is it currently worded?

204 | Secret not found

How should it be worded?

404 | Secret not found

Screenshots

Additional context

Related to #1636 where there is inconsistency across status codes on actors. Similar to secrets, suddenly 204 is being used instead of 404 or 400 here.

This is important, since 4xx or 5xx typically should throw an error, while 2xx should return a response (albeit empty)