[v25.3.x] cloud_roles: plumb metrics_tag through refresh_credentials impls

[vbotbuildovich]

Backport of PR #30489

• Command: git cherry-pick -x 4f0f029
• Commits backported: 1
• Conflicts resolved: 1
• Commits skipped (already on target): 0
• Backport branch: ai-backport-pr-30489-v25.3.x-1778874959

Conflict details

• 4f0f029 (src/v/cloud_roles/refresh_credentials.cc): the impl constructor initializer list and following if-statement formatting diverged between dev and v25.3.x. Kept v25.3.x's compact if (auto ...; cond) single-line formatting while adding the new _metrics_tag{std::move(metrics_tag)} initializer that is the actual intent of the commit.

Fixes: #30504,

[vbotbuildovich]

Retry command for Build#84542

please wait until all jobs are finished before running the slash command

/ci-repeat 1
skip-redpanda-build
skip-units
skip-rebase
tests/rptest/tests/nodes_decommissioning_test.py::NodesDecommissioningTest.test_decommission_status

[vbotbuildovich]

CI test results

test results on build#84542

test_status	test_class	test_method	test_arguments	test_kind	job_url	passed	reason	test_history
FLAKY(FAIL)	NodesDecommissioningTest	test_decommission_status	null	integration	https://buildkite.com/redpanda/redpanda/builds/84542#019e2d52-6a34-4237-9bcb-bef55751f7e0	9/11	Test FAILS after retries.Significant increase in flaky rate(baseline=0.0000, p0=0.0000, reject_threshold=0.0100)	https://redpanda.metabaseapp.com/dashboard/87-tests?tab=142-dt-individual-test-history&test_class=NodesDecommissioningTest&test_method=test_decommission_status
FLAKY(PASS)	RpkClusterTest	test_upload_and_query_cluster_license_rpk	null	integration	https://buildkite.com/redpanda/redpanda/builds/84542#019e2d52-6a30-44a5-aeae-fc7fe5cc3802	10/11	Test PASSES after retries.No significant increase in flaky rate(baseline=0.0000, p0=1.0000, reject_threshold=0.0100. adj_baseline=0.1000, p1=0.3487, trust_threshold=0.5000)	https://redpanda.metabaseapp.com/dashboard/87-tests?tab=142-dt-individual-test-history&test_class=RpkClusterTest&test_method=test_upload_and_query_cluster_license_rpk