Changed grant_type=AUTHORIZATION_CODE for grant_type=authorization_code

## What does this MR do?

Changed grant_type=AUTHORIZATION_CODE for grant_type=authorization_code 

## Why was this MR needed?
Using the example when provided the parameter grant_type=AUTHORIZATION_CODE the server returns a error:
```json 
{"error":"unsupported_grant_type","error_description":"The authorization grant type is not supported by the authorization server."}
```


See merge request !5539

Also a couple of minor edits for this branch are included

Simpler two queries than one JOIN with subquery

This is a follow up from !5347

Originally it was:

``` ruby
pipeline = pipelines.latest_successful_for(ref)
builds.where(pipeline: pipeline).latest.with_artifacts
```

However MySQL would complain that we can't use `IN` against a subquery which has `LIMIT`. Using `INNER JOIN` would be a workaround, however, doing that is too complicated in current version of Rails.

So let's just use two queries in this case.

Closes #14419

See merge request !5388