Add support for Pleroma/Akkoma roles

[kkostov]

In #270 we've added support for Mastodon's Roles.

[technicat]

Note besides the Account.role added in #270 there is also an Account.roles which I didn't implement because it's not in the API doc yet and I only see an empty list so far, but from the Mastodon source looks like it should be an array of Account, e.g. from the account_verify_credentials_condensed.json test case:

"roles" : [

  ],
  "followers_count" : 417,
  "note" : "<p>Lorem ipsum</p>",
  "avatar" : "https://example.com/avatars/person.jpeg",
  "display_name" : "person",
  "created_at" : "2023-02-07T00:00:00.000Z",
  "noindex" : false,
  "role" : {
    "id" : "-99",
    "permissions" : "65536",
    "highlighted" : false,
    "name" : "",
    "color" : ""
  },

[technicat]

btw, I also didn't include the boolean Account.group property, which is documented since Mastodon 3.1 but I'm still not clear what's a "Group actor"