Investigate and optimize ineffeciencies in backend /user-operator API routes

[dleard]

Blocked by #1062

The results of our load testing showed that we have some very ineffecient API routes in the /user-operator paths. We need to investigate the user-operator endpoints and optimize where necessary. Some really good exploration & optimization work has been done in #814, which will include documentation on the Django Silk endpoint profiler and some examples of how the GET /operations route was optimized.

AC:

• All user-operator endpoints have been investigated with the Silk profiler
• Optimizations to any ineffecient routes have been implemented
• Local load testing has been run on the routes as a check that performance has improved (We will load test in the dev environment again once this card and #825 are complete)

Note: There's a double user lookup happening in some endpoints. More details here: https://github.com/orgs/bcgov/projects/122/views/2?filterQuery=user&pane=issue&itemId=59071266. Completing this card may also complete the linked card.

[dleard]

The least efficient endpoints: /user-operators and /user-operators/{id} have been optimized. The rest of the endpoints will need to be profiled & optimized if necessary

[nanyangpro]

This will be refined. @andrea-williams