admin.apps API Methods

[acconrad]

Adds the admin.apps methods to the documentation store:

• https://api.slack.com/methods/admin.apps.approve
• https://api.slack.com/methods/admin.apps.restrict

Note that I added in 2 additional fields (not yet used):

• response - providing sample output for what you would expect to get back from the API
• warnings - separate issues from errors that do not block a successful return of the request

If you're okay with this format, I'll add in an additional PR to the documentation.ex file to include these 2 new fields and parse them properly.

Note that the purpose of this PR is to illustrate an updated way of handling the API methods with additional fields. Once this is approved I'd like to know if it's okay to update the remaining methods since many of them are deprecated, incomplete, or out-of-date.

[BlakeWilliams]

I like the idea of the response + warning fields so totally okay with that on my end. 👍