Enables group api to search by custom attribute and to return custom_attributes

[Jenson3210]

Fixes #1098 + Added integration tests

[jmini]

Can you please update the group.json in the test suite, so that your addition to the model is tested/used.

gitlab4j-api/src/test/java/org/gitlab4j/api/TestGitLabApiBeans.java

Lines 369 to 373 in 6c06521

	@Test
	public void testGroup() throws Exception {
	Group group = unmarshalResource(Group.class, "group.json");
	assertTrue(compareJson(group, "group.json"));
	}

[Jenson3210]

Added a custom attributes array

[Jenson3210]

any update here?

[jmini]

Sorry I had busy weeks at work and had no time to check updates in this repo.

[jmini]

I have rebased the source branch of this PR (6.x in the Jenson3210 fork) on top of main of this repo:

git rebase --onto origin/main origin/6.x
git push Jenson3210 HEAD:6.x --force

Be aware that your local branch 6.x has diverged with the one on the GitHub.
If you need to do one more changes on this branch:
I recommend to use git fetch and git reset --hard origin/6.x (assuming your local origin is pointing to the Jenson3210 fork on GitHub) before doing any local modifications instead of git pull.