Adding REFRESH_TOKEN_EXPIRE_SECONDS

[annagav]

What are the relevant tickets?

Related to #3142

Description (What does it do?)

Adds REFRESH_TOKEN_EXPIRE_SECONDS so that the cleartokens management command when run removes those refresh tokens whose lifetime is greater than the amount specified by REFRESH_TOKEN_EXPIRE_SECONDS settings.

How can this be tested?

Make sure you have tokens that are older than 1 month.

Run python manage.py cleartokens

Check that old tokens got removed.

[github-actions]

OpenAPI Changes

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[blarghmatey]

This needs to be nested under a namespaced dictionary object for it to take effect https://django-oauth-toolkit.readthedocs.io/en/latest/settings.html#settings

[cp-at-mit]

I'm not sure how many of these expired tokens we regularly accumulate between running this command, but if it's a lot should we consider adding the following:
To prevent the CPU and RAM high peaks during deletion process use CLEAR_EXPIRED_TOKENS_BATCH_SIZE and CLEAR_EXPIRED_TOKENS_BATCH_INTERVAL settings to adjust the process speed.