feat(helm): Make gateway container port configurable.

[kavirajk]

What this PR does / why we need it:

Avoid gateway container port being hard-coded and make it configurable. Default is still 8080 (previously hard-coded value).

Which issue(s) this PR fixes:
Fixes NA

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[chaudum]

I remember something that numbers in YAML may be rendered with scientific notation, e.g. 8.08e3 ... does this work with K8s?

[chaudum]

Nevermind, I think this was related to something else (printf)

[kavirajk]

Not aware of that. Will check it in local and confirm before merging. Thanks for the heads up.

[kavirajk]

template rending just fine (custom port 8081)

helm template loki ./ --values distributed-values.yaml | rg nginx -A 4

        - name: nginx
          image: docker.io/nginxinc/nginx-unprivileged:1.24-alpine
          imagePullPolicy: IfNotPresent
          ports:
            - name: http-metrics
              containerPort: 8081

Also rendering default without any overrides.

 - name: nginx
          image: docker.io/nginxinc/nginx-unprivileged:1.24-alpine
          imagePullPolicy: IfNotPresent
          ports:
            - name: http-metrics
              containerPort: 8080