Fix response code for nonexistent attachment

[noahshaw11]

Overview

Currently, a DELETE request for a non existent attachment responds with a 200 OK even if the attachment is missing. This PR changes the response code for nonexistent attachments to a 404 NOT FOUND {"error":"not_found","reason":"Document is missing attachment"}

Testing recommendations

% curl -X PUT http://localhost:15984/demo/38 -H 'Authorization: Basic YWRtOnBhc3M=' -d '{"name": "whatever"}'
{"ok":true,"id":"38","rev":"1-a0f595984a7c4cf1dafc4cf4c04081d6"}
% curl -X DELETE 'http://adm:pass@localhost:15984/demo/38/notexisting.txt?rev=1-a0f595984a7c4cf1dafc4cf4c04081d6'
{"error":"not_found","reason":"Document is missing attachment"}

Related Issues or Pull Requests

Deleting not existing attachment responds 200 instead of 404: #2146

Checklist

• Code is written and works correctly
• Changes are covered by tests
• Any new configurable parameters are documented in rel/overlay/etc/default.ini
• A PR for documentation changes has been made in https://github.com/apache/couchdb-documentation

[nickva]

+1

Flaky test is flaky:

[2021-07-19T17:20:48.690Z] UsersDbTest

[2021-07-19T17:20:48.690Z]   * test users password requirements
  * test users password requirements (117.3ms)

[2021-07-19T17:20:54.751Z]   * test users db
  * test users db (5046.5ms)

[2021-07-19T17:20:54.751Z] 

[2021-07-19T17:20:54.751Z]   1) test users db (UsersDbTest)

[2021-07-19T17:20:54.751Z]      test/elixir/test/users_db_test.exs:104

[2021-07-19T17:20:54.751Z]      Assertion with != failed, both sides are exactly equal

[2021-07-19T17:20:54.751Z]      code: assert ddoc.body()["validate_doc_update"] != nil

[2021-07-19T17:20:54.751Z]      left: nil

[2021-07-19T17:20:54.751Z]      stacktrace:

[2021-07-19T17:20:54.751Z]        test/elixir/test/users_db_test.exs:108: (test)

Not related to the code. May have to just retry force pushing a few times