Bump Prometheus to 2.38.0

What does this MR do?

This MR bumps Prometheus for the chart to the same version as deployed via Omnibus. Omnibus includes Prometheus 2.38.0 while the Helm chart currently deploys 2.31.1.

Note: There is no Prometheus chart release defaulting to 2.38.0 so the latest Chart deploying the next highest app version was chosen. The image tag is overridden to 2.38.0.

Prometheus Chart Version	Prometheus App Version
15.0.0 < 15.5.4	2.31.1
15.5.4 < 15.10.4	2.34.0
15.10.4 < 15.15.0	2.36.2
15.15.0 < 15.18.0	2.39.1

Related issues

Closes #4083 (closed)

Test Plan

1. Deploy the chart with the changes of this MR
2. Verify the deployed Prometheus image

> kubectl get pods <PROM_POD> -o yaml | yq .spec.containers[1].image
quay.io/prometheus/prometheus:v2.38.0

3. Verify Prometheus scrapes metrics successfully (e.g. via the UI by adding a ingress beforehand)

prometheus:
  server:  
    ingress:
      enabled: true
      hosts:
        - <HOST_NAME>

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.