expose server configuration for all GC intervals

The [`job_gc_threshold`](https://www.nomadproject.io/docs/configuration/server#job_gc_threshold) controls how often the core job for garbage collecting Jobs runs. But we also have GC jobs for Evals, Nodes, Deployments, CSIPlugins, CSIVolumeClaims, and OneTimeTokens. We currently expose the threshold configuration for these jobs but not the interval, but it seems like it could be handy for some users to have fine-grained control over this.

Start with the server configuration entry for job_gc_threshold in the Nomad configuration documentation, then trace the existing interval and threshold settings for the Eval, Node, Deployment, CSIPlugin, CSIVolumeClaim, and OneTimeToken garbage-collection jobs. Done means each listed job exposes a fine-grained interval configuration alongside its existing threshold setting.

Written by the indexing model from the issue text.