fix: prometheus client - use service-ca file for TLS

[tremes]

I came across this when I was experimenting with openshift/openshift-mcp-server#124 when I was facing the unsigned cert issue when calling get_alerts tool.

[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

[iNecas]

makes sense, is consistent with the configuration we do in

obs-mcp/pkg/mcp/auth.go

Line 33 in 84c5bb6

defaultServiceAccountCAPath = "/var/run/secrets/kubernetes.io/serviceaccount/service-ca.crt"

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: iNecas, tremes

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [iNecas]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[iNecas]

/lgtm