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/serviceAccount/serviceAccount.yaml

@@ -53,13 +53,13 @@ tests:
   asserts:
   - hasDocuments:
       count: 1
-  - exists:
+  - isSubset:
       path: metadata.annotations
-      value:
+      content:
         foo: bar
-  - exists:
+  - isSubset:
       path: metadata.labels
-      value:
+      content:
         bar: foo
   - equal:
       path: metadata.name