Code review comment for ~ines-almeida/launchpad-buildd:update-close-session-for-fetch-service

Given we will have 2 endpoints (one for token revocation, another for session closing), I decided to separate this into 2 MPs:
 - This one will handle adding the logic to call the revocation endpoint to the fetch service
 - The next one will handle closing the fetch service session and saving the data (to be opened)