[DO] Token endpoint

[gonzaloriestra]

Related to #15077

[simon-contreras-deel]

👍

[alrocar]

If I'm not wrong we added this issue to avoid having to call central for the token.

Right now, I think we can try with the current approach in this PR. It will add a little bit more of latency but since the whole process is batch and it happens once every hour I think it's fine.

[gonzaloriestra]

@alrocar I thought we changed the approach when we decided to use the short-lived access tokens, but I guess we could sync the key anyway and request the token directly from cartodb. Anyway, yes, we can improve it in the next iteration.

[alrocar]

@gonzaloriestra sure, no problem. Let's move forward!

[simon-contreras-deel]

Acceptance 🍏

• fails without api_key
• fails with random apikey
• works getting token with master
• works getting token with regular api key
• fails getting token with regular api key without do permissions
• works getting token with oauth api key
• fails getting token with oauth api key without do permissions
• can show the user dataset using the token https://www.googleapis.com/bigquery/v2/projects/{customers-project}/datasets?access_token={access-token}