Begin 2.x release train

[bitwiseman]

Description

I would love for github-api v2.x to be a larger change that has major new features.

However, the most pressing need is clearing technical debt for better stability and ease of adding new features. These changes break binary compatibility requiring a major version bump.

v2.0 includes:

• Drop support for Java 8
• Remove functional dependencies on HttpURLConnection
• Remove most deprecated classes and methods
• Remove all "bridge methods"

Before submitting a PR:

• Changes must not break binary backwards compatibility. If you are unclear on how to make the change you think is needed while maintaining backward compatibility, CONTRIBUTING.md for details.
• Add JavaDocs and other comments explaining the behavior.
• When adding or updating methods that fetch entities, add @link JavaDoc entries to the relevant documentation on https://docs.github.com/en/rest .
• Add tests that cover any added or changed code. This generally requires capturing snapshot test data. See CONTRIBUTING.md for details.
• Run mvn -D enable-ci clean install site locally. If this command doesn't succeed, your change will not pass CI.
• Push your changes to a branch other than main. You will create your PR from that branch.

When creating a PR:

• Fill in the "Description" above with clear summary of the changes. This includes:
  • If this PR fixes one or more issues, include "Fixes #" lines for each issue.
  • Provide links to relevant documentation on https://docs.github.com/en/rest where possible. If not including links, explain why not.
• All lines of new code should be covered by tests as reported by code coverage. Any lines that are not covered must have PR comments explaining why they cannot be covered. For example, "Reaching this particular exception is hard and is not a particular common scenario."
• Enable "Allow edits from maintainers".

[codecov]

Codecov Report

Attention: Patch coverage is 81.18812% with 19 lines in your changes missing coverage. Please review.

Project coverage is 82.61%. Comparing base (9e9e775) to head (b868261).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...hsuke/github/extras/HttpClientGitHubConnector.java	83.33%	4 Missing and 1 partial ⚠️
src/main/java/org/kohsuke/github/GHMyself.java	0.00%	4 Missing ⚠️
...ava/org/kohsuke/github/GitHubRateLimitHandler.java	76.47%	3 Missing and 1 partial ⚠️
...c/main/java/org/kohsuke/github/GHOrganization.java	25.00%	3 Missing ⚠️
...va/org/kohsuke/github/GitHubAbuseLimitHandler.java	90.47%	2 Missing ⚠️
src/main/java/org/kohsuke/github/GitHubClient.java	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1935      +/-   ##
============================================
+ Coverage     81.36%   82.61%   +1.24%     
+ Complexity     2465     2323     -142     
============================================
  Files           239      231       -8     
  Lines          7475     6977     -498     
  Branches        402      376      -26     
============================================
- Hits           6082     5764     -318     
+ Misses         1146      975     -171     
+ Partials        247      238       -9     

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[bitwiseman]

@ihrigb
Noted that this was not marked as Deprecated.

Did a search on usages:
https://github.com/search?q=org%3Ajenkinsci+getPullRequests+path%3A%2F%5Esrc%5C%2Fmain%5C%2Fjava%5C%2F%2F+org.kohsuke.github&type=code

It looks like there's at least one usage in the wild, and since it is in Jenkins it will cause breaks for some time to come.
https://github.com/jenkinsci/ghprb-plugin/blob/master/src/main/java/org/jenkinsci/plugins/ghprb/GhprbRepository.java#L145

There's a similar one for listPullRequests().

Might consider bringing these back at least as bridge methods to not break Jenkins plugins. On the other hand this is a 2.0, accepting some breakages might be acceptable.