build: Add rpm-signature-scan task for Konflux pipeline #825

Namespace: <a href="https://detailurl.setting.custom-console-url-namespace.is.not.configured" rel="nofollow">insights-management-tenant
PipelineRun: <a href="https://console.redhat.com/application-pipeline/ns/insights-management-tenant/pipelinerun/provisioning-backend-on-pull-request-7mxrj" rel="nofollow">provisioning-backend-on-pull-request-7mxrj

Success

Red Hat Konflux/provisioning-backend-on-pull-request has successfully validated your commit.

Status	Duration	Name
✅ Succeeded	6 seconds	init
✅ Succeeded	2 minutes	clone-repository
✅ Succeeded	3 minutes	build-container
✅ Succeeded	1 minute	rpms-signature-scan
✅ Succeeded	1 minute	build-image-index
✅ Succeeded	37 seconds	sast-snyk-check
✅ Succeeded	17 seconds	push-dockerfile
✅ Succeeded	50 seconds	clair-scan
✅ Succeeded	1 minute	clamav-scan
✅ Succeeded	8 seconds	apply-tags
✅ Succeeded	1 minute	deprecated-base-image-check
✅ Succeeded	2 minutes	ecosystem-cert-preflight-checks
✅ Succeeded	58 seconds	show-sbom
✅ Succeeded	59 seconds	show-summary