chore: update self-monitor image to prom 3.8.0

[a-thaler]

Description

Changes proposed in this pull request (what was done and why):

• update self-monitor image to prom 3.8.0

Changes refer to particular issues, PRs or documents:

Traceability

• The PR is linked to a GitHub issue.
• The follow-up issues (if any) are linked in the Related Issues section.
• If the change is user-facing, the documentation has been adjusted.
• If a CRD is changed, the corresponding Busola ConfigMap has been adjusted.
• The feature is unit-tested.
• The feature is e2e-tested.