[FEATURE] Create REST APIs to list all registered jobs and get jobs actively running in the cluster

[cwperks]

Is your feature request related to a problem?

Currently, job-scheduler has REST APIs, but they are only applicable in the context of extensions and not for OpenSearch plugins.

As an OpenSearch operator, I would like APIs to interact with the job-scheduler to see all registered jobs in my cluster, what the job type is, whether it is enabled/disabled, the job's schedule and when it was last run.

Additionally, I would like another API to fetch information about jobs actively running in the cluster, where they are running and total time elapsed.

What solution would you like?

Create 2 new REST APIs to:

1. Get all registered jobs
2. Get information about currently running jobs

I could imagine that in the future that job-scheduler could better keep track of job history with stats and then also get more administrative APIs that limit where jobs can run in a cluster to give cluster admins more control.