Fix blackbox exporter Probe reconciliation flapping

[ygalblum]

Summary

The odf-blackbox-exporter Probe is continuously updated every reconcile
cycle (generation 11550+ in ~48h) because controllerutil.CreateOrUpdate
detects a perpetual diff between the desired state and the server-returned
state. Two CRD-defaulted fields cause the drift:

1. ProberSpec.Path: the Probe CRD defaults this to "/probe", but
   the code never sets it. Each reconcile overwrites "/probe" with "",
   triggering an Update that the API server re-defaults.

2. bearerTokenSecret: the API server materializes an empty
   {key: "", name: ""} via CRD structural schema defaults for
   SecretKeySelector. The desired spec has this field nil, creating a
   constant diff. prometheus-operator then rejects the Probe with
   "resource name may not be empty".

Changes

• Explicitly set ProberSpec.Path: "/probe" in the desired Probe spec to
  match the CRD default, eliminating the Path drift.
• Preserve the server-returned bearerTokenSecret in the mutate function
  when the desired spec does not set one, preventing the nil-vs-empty diff
  from triggering an Update.
• Update test to assert on the Path value.

Test plan

• go build ./... — compiles
• go test ./internal/controller/storagecluster/... -run TestCreateBlackboxProbe — passes
• go vet ./... — no issues
• Deploy on a cluster with the blackbox exporter enabled and verify the
  Probe generation counter stabilizes (no longer climbs every reconcile)
• Verify prometheus-operator no longer logs
  "resource name may not be empty" for the Probe

[openshift-ci]

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This pull-request has been approved by: ygalblum
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[openshift-ci]

Hi @ygalblum. Thanks for your PR.

I'm waiting for a red-hat-storage member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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