move eso-grafana-oidc to conditional component

What does this MR do and why?

Move eso-grafana-oidc external secret to a conditional component of keycloak-oidc-external-secrets unit. This secret will be produced only when monitoring unit is enabled.

Related reference(s)

closes #1314 (closed) closes #1324 (closed)

Test coverage

On a failed libvirt metal deployment with monitoring unit disabled, an apply.sh with this code solves the issue.