Investigate and optimize all backend API routes

[dleard]

Blocked by #1061

The results of our load testing showed that we have some very ineffecient API routes in the /operations and /user-operator paths. We have created #825 and #826 to tackle the troublesome paths right away as they are blocking our path to prod. The rest of the endpoints appeared to perform well during load testing, but we should (post-release) give all of these API routes a look with the Django Silk endpoint profiler to see if there are any other minor optimizations that we can implement.

This card is a placeholder and should probably be broken up in a way similar to how the k6 tests were done (operator, user, others).

We should also look into making a check with the profiler part of our AC when submitting PR that adds or makes changes to an API endpoint in the backend. Or even better, look at how we might automate this check with some bounds or thresholds.

Note by Sepehr:

• All 4 endpoints mentioned in ticket 1061 are already optimized (by caching their results) and no need to optimize them more.

AC:

• This card has been broken up in a way that makes sense to complete the profiling work

[Dianadec]

placeholder card that should probably be split up. cc @dleard

[nanyangpro]

Re: Refinement discussion - This one is more like an epic. Once we have individual tickets identified, this one will be gone.

[dleard]

This can be better defined once #952 and #1061 are complete. Having our API structure split up first will make it easier to write individual cards for each endpoint.

[nanyangpro]

This will be refined. @andrea-williams