Show moderator statistics similar to users

[blainsmith]

Current there is the usage.users object with the number of users on the node. Recently, I saw a post from someone wishing to know how many moderators were on the node as well. Given that content moderation is becoming a hot topic as ActivityPub and ATProto protocols getting more usage folks might be making choices on whether to join a node or not based on the content and moderation policies. I thought this would be a good opportunity to expose a similar statistic.

  "usage": {
    "users": {
      "total": 1629,
      "activeMonth": 1629,
      "activeHalfyear": 1629
    },
    "mods": {
      "total": 5,
      "activeMonth": 2,
      "activeHalfyear": 4
    }
  }

Adding an additional mods key with the same object structure as users nodes can populate those to include moderator statistics. The users key would still INCLUDE the moderator statistics so it is backwards compatible with current usage. This would then allow folks to display totals, ratios, etc. however they see fit.