fix(secret): enforce basic auth credentials

This patch remove generation of a random string for the username and password of
the basic auth credentials.

The problem with the random generated basic auth credentials is, that this leads
to a new shasum of the secret. GitOps tools like ArgoCD detects a drift trigger
a rolling update.

To avoid this must now the basic auth credentials be defined to enable
prometheus metrics.

unittests/deployment/prometheusServiceMonitor.yaml

@@ -13,6 +13,8 @@ tests:
   set:
     prometheus.metrics.enabled: true
     prometheus.metrics.serviceMonitor.enabled: true
+    prometheus.metrics.secret.new.basicAuthPassword: "my-password"
+    prometheus.metrics.secret.new.basicAuthUsername: "my-username"
   asserts:
   - exists:
       path: spec.template.metadata.annotations.checksum/secret-reposilite-unittest-basic-auth-credentials