Discoverers: Improve command-line flags and command-line flag documentation or help text

[alexbrand]

Some of the flags are not specific enough, while others could get a better description.

Some I have stumbled on:

• num-threads: number of threads for what?
• http-client-timeout: which HTTP client?

Maybe flag docs/descriptions could get a review from @Bradamant3

[alexbrand]

One consideration to keep in mind if we decide to change flags is whether we want to remain backwards compatible with previous deployment manifests.