chore: extend securitypolicy with backendRef attribute

[andibeuge]

For securityPolicies OIDC counter parts we can use internal traffic, if the system is run within the same cluster. If not set, gateway tries to derive the backend dynamically from the url which might not work depending on the loadbalancer being used for the auth system.

[Copilot]

Pull request overview

Adds support for explicitly configuring backendRefs on Envoy Gateway SecurityPolicy resources so OIDC and JWT JWKS retrieval can be routed to an in-cluster IdP service instead of relying on URL-based backend derivation.

Changes:

• Introduces envoy.security.backendRefs (global) and envoy.security.policies[].backendRefs (per-policy override) in example values.
• Renders backendRefs into spec.oidc.provider and spec.jwt.providers[].remoteJWKS when configured.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
parcellab/monolith/values.yaml	Documents global and per-policy backendRefs configuration in the monolith chart values.
parcellab/microservice/values.yaml	Documents global and per-policy backendRefs configuration in the microservice chart values.
parcellab/common/templates/_securitypolicies.tpl	Implements templating to emit backendRefs in OIDC provider and JWT remoteJWKS blocks.