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

[Erik Joelsson]

> 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

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Changes:
  - all: https://git.openjdk.org/skara/pull/1573/files
  - new: https://git.openjdk.org/skara/pull/1573/files/17f3f8b4..0767eb2a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1573&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1573&range=00-01

  Stats: 48 lines in 6 files changed: 44 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1573.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1573/head:pull/1573

PR: https://git.openjdk.org/skara/pull/1573