Add tootctl domains crawl

[Gargron]

Usage:
  tootctl domains crawl [START]

Options:
  c, [--concurrency=N]          
                                # Default: 50
  s, [--silent], [--no-silent]  
  f, [--format=FORMAT]          
                                # Default: summary

Description:
  Crawl the fediverse by using the Mastodon REST API endpoints that expose all known
  peers, and collect statistics from those peers, as long as those peers
  support those API endpoints. When no START is given, the command uses this
  server's own database of known peers to seed the crawl.

  The --concurrency (-c) option controls the number of threads performing HTTP
  requests at the same time. More threads means the crawl may complete faster.

  The --silent (-s) option controls progress output.

  The --format (-f) option controls how the data is displayed at the end. By
  default (`summary`), a summary of the statistics is returned. The other
  options are `domains`, which returns a newline-delimited list of all
  discovered peers, and `json`, which dumps all the aggregated data raw.