[OSSM-8128] Use comunity prometheus operator

[mkralik3]

• Changed custom prometheus to comunity one ( since the RH one is not available anymore, see the jira ticket )
• Refactored installing of custom prometheus to use the same way as Tempo or certmanager

TestCustomPrometheus test passed: https://master-jenkins-csb-servicemesh.apps.ocp-c1.prod.psi.redhat.com/job/maistra/job/maistra-test-tool/2759/

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[unsortedhashsets]

LGTM, like that refactoring to separate operator install from test 👍