fix: ensure Helm chart values are aligned with templates

[nepalevov]

Key changes:

• removed forecastle.container.securityContext support and merging logic with forecastle.deployment.securityContext; seemed like legacy stuff, clear usage of forecastle.deployment.securityContext remains untouched
• moved forecastle.namepace value to namepace - a fix so namespace can actually be overridden, currently no-op
• added values that are referenced in templates, but missing in values.yaml for visibility:
  • nameOverride
  • forecastle.deployment.imagePullSecrets
  • ingress.tls

Minor enhancements:

• removed forecastle.proxy value - not referenced in templates
• moved default value for openshiftOauthProxy.image from template to values.yaml for visibility
• values.yaml formatting
• added .gitignore to exclude helm-unittest artifacts
• added helm unit tests to cover changes