Build API key: don't fetch and validate key twice

[stsewd]

There is some noticeable time increase when hitting our APIs using a token. We can also look into changing the hashing algorithm florimondmanca/djangorestframework-api-key#173 (comment) later.

Instead of relying on the parent method,
we just now override the whole method to have
access to the key itself.

[benjaoming]

It makes sense to not call the parent method and doing the same database queries again 👍

It's a bit silly that it has to be overwritten with almost identical code, but the parent methods weren't written to make it easy to get the key otherwise :(