Graduate review requests to what eventually shipped

[shiftkey]

Resolves #2122

This is a breaking change in several ways due to changes the API made while under preview:

• requesting teams is now supported, so the response and requests payload had to change
• pagination is no longer supported, so those overloads have been removed

To use the new API there are two static constructors to differentiate between "request users" and "request teams":

// request specific collaborators
var collaborators = new List<string> { "shiftkey", "ryangribble" };
var requestCollaborators = PullRequestReviewRequest.ForReviewers(collaborators);

// request specific teams
var teams = new List<string> { "frontend-reviewers", "backend-reviewers" };
var requestTeams = PullRequestReviewRequest.ForTeamReviewers(teams);

// request a mixture of both
var requestBothGroups = new PullRequestReviewRequest(collaborators, teams);

[codecov]

Codecov Report

Merging #2153 into master will decrease coverage by 0.1%.
The diff coverage is 37.93%.

@@            Coverage Diff             @@
##           master    #2153      +/-   ##
==========================================
- Coverage   66.82%   66.71%   -0.11%     
==========================================
  Files         544      545       +1     
  Lines       14234    14233       -1     
==========================================
- Hits         9512     9496      -16     
- Misses       4722     4737      +15

Impacted Files	Coverage Δ
Octokit/Helpers/AcceptHeaders.cs	100% <ø> (ø)	⬆️
Octokit/Models/Response/RequestedReviews.cs	0% <0%> (ø)
Octokit/Clients/PullRequestReviewRequestsClient.cs	100% <100%> (+11.76%)	⬆️
...ients/ObservablePullRequestReviewRequestsClient.cs	100% <100%> (ø)	⬆️
Octokit/Models/Request/PullRequestReviewRequest.cs	55.55% <50%> (-4.45%)	⬇️
Octokit.Reactive/Helpers/ObservableExtensions.cs	91.26% <0%> (-1.95%)	⬇️

[ch1seL]

@shiftkey Thank you 👍

[shiftkey]

release_notes: updated client.PullRequest.ReviewRequest to reflect what is currently supported

[shiftkey]

advisories: due to the Review Request API graduating from preview there are some breaking changes that will impact callers:

• client.PullRequest.ReviewRequest.GetAll() has been removed in favour of client.PullRequest.ReviewRequest.Get() as there is no pagination support for the API
• client.PullRequest.ReviewRequest.Get() now returns a RequestedReviews object that contains users and teams
• PullRequestReviewRequest now accepts teams, and helper functions are added to make it clear whether a request review is for users or teams

Example code:

// request specific collaborators
var collaborators = new List<string> { "shiftkey", "ryangribble" };
var requestCollaborators = PullRequestReviewRequest.ForReviewers(collaborators);

var number = 123;

await client.PullRequest.ReviewRequest.Create("owner", "repo", number, requestCollaborators);

var reviewers = await client.PullRequest.ReviewRequest.Get("owner", "repo", number);

Console.WriteLine($"Review {number} has requested {reviewers.Users.Count} user reviews and {reviewers.Teams.Count} team reviews");