feat: add extraEnv for httpbingo chart

[plumdog]

Purpose

#142

Changes

• add extraEnv to values. This defaults to {}, but allows setting env vars, namely https://github.com/mccutchen/go-httpbin#configuration

Testing

$ helm template . --set extraEnv.FOO=bar | yq '. | select(.kind == "Deployment") | .spec.template.spec.containers[0].env'
- name: FOO
  value: "bar"

Code Author Checklist

• Bump the chart version (Chart.yaml -> version)
• JSON Schema updated (values.schema.json) - ❗ n/a, no such file for this chart
• Update README.md via helm-docs (or make prep)
  • no, I get an error: make: helm-docs: No such file or directory
• Run pre-commit run --all-files via pre-commit (or make prep)
• Update Artifacthub annotation (Chart.yaml -> artifacthub.io/changes, artifacthub.io/images)