refactor(Coder plugin): update workspace queries to use updated API endpoint definitions

[Parkreiner]

Closes #60

Not quite as much of a win on the performance side as I would've hoped, but on the bright side, it does remove the need for a bunch of code that was only here because of the previous API limitations

Changes made

• Updates the getWorkspacesByRepo function exposed by CoderClient to use the updated API endpoints
• Removes all code around checking build parameters, since we no longer need to make requests for the build parameters at all
• Updates tests and mock server logic to account for more data getting threaded through the single /workspaces endpoint

Notes

• The changes here depend on the PRs for #124 and #125. Probably best to wait until those have been approved before seriously going through this code

[Parkreiner]

@Kira-Pilot Changes should be ready now!