[loadtest] Add a loadtest for SCD to the existing Locust infrastructure.

[BradNicolle]

This PR:

• Updates the existing load test USS client to work with the current version of Locust, by using the included client from HttpUser rather than reimplementing this in DSSClient. It then just simply configures the auth function to use the AuthAdapter.
• Adds a name argument to each call to client, which allows calls to the same API to be grouped together in the Locust UI (i.e. rather than a separate entry for each random UUID).
• Adds some geo_utils to simplify creation of a flight path, by randomly orienting a set of rectangles of random length at a random start point roughly within a given geographical radius.
• Adds an SCD load test which just creates intents with these random flight paths.
  • It does not currently implement OVN tracking.
  • OVN tracking would be simple to add for a single Locust process, but multi-process or multi-machine might require communicating across nodes if we want to completely avoid 409s.
  • In-memory OVN tracking might be sufficient if we can tolerate a low proportion of 409s.