api: Grant Indexes

[R2ZER0]

This PR creates database indexes on the new Grant convenience fields to finish the work of improving API GrantMadeView and GrantReceivedView performance.

[R2ZER0]

It looks like the tests are failing, because the new indexes rely on the btree_gin¹ postgres extension. Django tries to create it, but only superusers can create the extension: https://github.com/ThreeSixtyGiving/datastore/actions/runs/8333672434/job/22805632982?pr=198

I guess we'll have to check that we're happy to use it, and then enable the extension in salt config.

Footnotes

1. https://www.postgresql.org/docs/12/btree-gin.html ↩

[R2ZER0]

I tried fixing the tests by manually installing the extension into the 360givingdatastore test db w/ psql, but Django creates it's own temporary database to run the tests in instead. The only feasibly way I could think of to fix it then was to give the test user superuser so Django can create the extension itsself.