[v25.2.x] [UX-508] added json/yaml formatting to rpk group describe command

[vbotbuildovich]

Backport of PR #27647

[r-vasquez]

@alextreichler Holding this for now. Let me know if it's needed for 25.2. Current DEV contains changes to the current output (adding the coordinator-node) and I would like it to be deployed in the next major version.

[vbotbuildovich]

CI test results

test results on build#73876

test_class	test_method	test_arguments	test_kind	job_url	test_status	passed	reason	test_history
RandomNodeOperationsTest	test_node_operations	{"cloud_storage_type": 1, "compaction_mode": "chunked_sliding_window", "enable_failures": true, "mixed_versions": false, "with_iceberg": false}	integration	https://buildkite.com/redpanda/redpanda/builds/73876#0199c9f3-8835-4422-b8c6-ed3c9f90c1c2	FLAKY	20/21	upstream reliability is '100.0'. current run reliability is '95.23809523809523'. drift is 4.7619 and the allowed drift is set to 50. The test should PASS	https://redpanda.metabaseapp.com/dashboard/87-tests?tab=142-dt-individual-test-history&test_class=RandomNodeOperationsTest&test_method=test_node_operations