fix: Move Prometheus validation stanza to local schema

[claudio-benfatto]

Related issue

Prometheus endpoint cannot be validated by local json schema

Gist of the issue

The current v0.38.0-beta.2 release has introduced prometheus metrics and the following configuration stanza:

serve:
  prometheus:
    port: 9000
    host: localhost
    metrics_path: /metrics

however the local config.schema.json does not contain it.
This is also the schema that is loaded on startup root.go which causes the command to fail with a validation error:

INFO[0000] Config file loaded successfully.              path=/etc/auth-oathkeeper/templates/oathkeeper.yaml
FATA[0000] The configuration is invalid and could not be loaded.  [config_key=serve]="additionalProperties \"prometheus\" not allowed" config_file=/etc/auth-oathkeeper/templates/oathkeeper.yaml

Proposed changes

The proposed change is to add the prometheus validation to the local schema

Checklist

• I have read the contributing guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further comments

I tested the compiled binary against an example configuration containing the prometheus stanza and everything works correctly

[CLAassistant]

All committers have signed the CLA.

[aeneasr]

Thank you! To prevent future regressions it would be great to have some tests for this, namely here. You can define the values over here. :)

[claudio-benfatto]

Thank you! To prevent future regressions it would be great to have some tests for this, namely here. You can define the values over here. :)

Hi @aeneasr thanks a lot for pointing me to the correct locations for the tests!

[aeneasr]

No problem :) This helps me so much when other maintainers do it so I try to replicate it :)

[aeneasr]

Thank you and sorry for the late merge!