Add support for --format=json flag to tctl bots add

[russjones]

Adding support for the --format=json flag for tctl bots add would be really useful for automation allowing the user of tools like jq to extract join information.

For example, tctl users add already supports this.

$ tctl users add foo --roles=access --logins=root --format=json
{
  "kind": "user_token",
  "sub_kind": "invite",
  "version": "v3",
  "metadata": {
    "name": "00000000000000000000000000000000",
    "expires": "2022-03-03T05:38:07.971830993Z"
  },
  "spec": {
    "user": "foo",
    "url": "https://proxy.example.com:3080/web/invite/00000000000000000000000000000000",
    "created": "2022-03-03T04:38:07.971831423Z"
  }
}

[timothyb89]

I've added this in #10833:

$ tctl bots add test --roles=access --format=json
{
  "user_name": "bot-test",
  "role_name": "bot-test",
  "token_id": "2a7bdabdb9225e0fdf83df5de0bf94a0",
  "ttl": 3599998522147,
  "join_method": "token"
}