RFR: 2069: Add group and collaborator methods to Forge and HostedRepository [v2]

[Zhao Song]

On Fri, 20 Oct 2023 14:05:35 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> This patch adds some new methods on Forge and HostedRepository to interact with forge groups and repository collaborators respectively. It also adds a lot more possible customization to the test class `CensusBuilder` as well as adding some missing `final` declarations in test classes. All the new API calls have manual tests added. It's quite large for what it is, but isn't really affecting any current production code.
>
> Erik Joelsson has updated the pull request incrementally with one additional commit since the last revision:
> 
>   copyright

Looks very good!

-------------

Marked as reviewed by zsong (Reviewer).

PR Review: https://git.openjdk.org/skara/pull/1573#pullrequestreview-1690522014