Chart refactor with breaking changes

[johnjeffers]

This PR hardens and reorganizes the FusionAuth Helm chart:

• Splits chart helper logic into focused database, deployment, labels, search, and init-container templates.
• Adds structured database credential values under database.dbUser.* and database.rootUser.*
• Adds search.basicAuth.* values, including existing-secret support (closes Add existingSecret for elasticsearch #125)
• Prevents environment from overriding chart-managed settings.
• Adds validation for conflicting reserved names, invalid credential combinations, ingress requirements, HPA configuration, PDB configuration, and kickstart data.
• Removes service.spec support and ExternalName service support to prevent invalid service configurations.
• Updates supported Kubernetes APIs to require Kubernetes >=1.23.
• Removes the low-value Helm test connection hook.
• Generates chart README from template chart/README.md.gotmpl using helm-docs.
• Adds helm unittest coverage for database, search, init-container, and negative validation behavior.
• Adds CI workflows for chart tests, unit test matrix, and generated docs verification.
• Updates release packaging to stamp dev placeholders with release chart/app versions.

Breaking / Upgrade Notes

• Minimum Kubernetes version is now 1.23.
• service.spec has been removed.
• service.type=ExternalName is no longer supported.
• Chart-managed database Secrets changed from <release>-credentials to:
  • <release>-db-credentials
  • <release>-db-root-credentials
• Chart-managed environment variables can no longer be overridden through environment; use chart values instead.