Co-authored-by: Derek Strickland <1111455+DerekStrickland@users.noreply.github.com>

…into f-reload-num-schedulers

- add mutex for contended server data
    - `workerLock` for the `workers` slice
    - `workerConfigLock` for the `Server.Config.NumSchedulers` and
      `Server.Config.EnabledSchedulers` values
- add Copy() func for `SchedulerWorkerPoolArgs`
- refactor NewWorker to allow for creating an unstarted worker for testing

- Start, Pause, Resume, Stop for func names
- made setPause, shutdown implementing funcs for abobe functions
- updated tests

There are two places in the code where the scheduler worker code waits: to dequeue an eval and for a raft index