fix(operator): rename BackendAuthType enum value to camelCase

[tmchow]

The enum value `external_auth_config_ref` was the only snake_case type discriminator in the CRD codebase. Every other value uses camelCase (`tokenExchange`, `headerInjection`, `bearerToken`, `embeddedAuthServer`, `awsSts`, etc.). Renamed to `externalAuthConfigRef` for consistency before the API moves past v1alpha1.

Changes:

• Renamed the constant string value in `virtualmcpserver_types.go`
• Updated kubebuilder validation Enum markers and CEL validation rules
• Updated all test fixtures across 5 test files
• Regenerated CRD manifests and API docs

Build, lint (0 issues), and compilation all pass.

Fixes #4542

[jerm-dro]

Blocker: it looks like this is used as an enum value. Changing the value will cause existing CRDs to break. Please introduce a DeprecatedBackendAuthTypeExternalAuthConfigRef = external_auth_config_ref so that we can still handle the old CRDs correctly. We should log.Warn that this old value is deprecated whenever it's used.

[ChrisJBurns]

Was this something you were ok to release as a breaking change now, or something you wanted a gradual rollout of? @jerm-dro

[jerm-dro]

Is the cost of the deprecation approach low? If so, I'd prefer to deprecate instead of break.

[tmchow]

Added DeprecatedBackendAuthTypeExternalAuthConfigRef constant, updated kubebuilder enum to accept both values, updated validation switch. lmk if i misunderstood

[jerm-dro]

This looks like what I was imagining. I think you'll need to regenerate some stuff. We'll also want to log a warning about the deprecation when the deprecated value is used.

[codecov]

Codecov Report

❌ Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.91%. Comparing base (ffef243) to head (f831f0b).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/thv-operator/pkg/vmcpconfig/converter.go	22.22%	6 Missing and 1 partial ⚠️
...hv-operator/api/v1alpha1/virtualmcpserver_types.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4563      +/-   ##
==========================================
+ Coverage   68.86%   68.91%   +0.05%     
==========================================
  Files         505      505              
  Lines       52320    52387      +67     
==========================================
+ Hits        36028    36105      +77     
+ Misses      13504    13492      -12     
- Partials     2788     2790       +2     

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