feat: proxy sidecar injection and headless service discovery for embedded Infinispan

[Vaishnav88sk]

Description

This PR migrates the reshapr-proxy sidecar injection logic into reshapr-controllers and adapts it to support the new embedded Infinispan clustering architecture, dropping the legacy sticky-session requirements.

Key Changes

1. Mutating Admission Webhook (AdmissionControllers.java):

   • Injects the reshapr-proxy sidecar into pods annotated with io.reshapr/inject: "true".
   • Exposes the new JGroups (7778) and FD_SOCK2 (57778) ports on the proxy container.
   • Injects the JAVA_OPTS_APPEND environment variable with JGroups and Infinispan JVM arguments.
   • Sets the -Dreshapr.infinispan.dns-query flag to point to the headless service dynamically provisioned by the operator.

2. Companion Operator (DeploymentProxyReconciler.java):

   • Watches Deployment resources for the io.reshapr/inject: "true" annotation.
   • Automatically provisions and manages a dedicated headless service (clusterIP: None) named reshapr-proxy-<app-name> for each deployment.
   • This headless service enables DNS_PING cluster discovery so injected sidecars can seamlessly form their embedded JGroups cluster.

Related Issues/PRs

• Closes Migration of Kubernetes Admission Controller for Proxy Sidecar Injection #4
• Supersedes/Replaces feat: migrate proxy sidecar injection and add Deployment proxy reconc… #5
• Adapts architecture from reshapr-helm-charts issue reshaprio/reshapr-helm-charts#38
• Original webhook implementation from reshaprio/reshapr#147