feat: HTTP healthcheck on EKS GatewayServer

[fra98]

Description

• Remove the dedicated EKS gateway server template and unify into the single standard template. Instead of maintaining a separate Helm template for EKS, the EKS-specific NLB annotations (healthcheck config, load balancer type, scheme, etc.) are now injected via liqoctl install eks values.
• Add ServiceAnnotations and ServiceLabels fields to the GatewayServer CRD, allowing users to customize the gateway Service metadata directly from the CR spec without modifying the server template.
• Switch EKS healthcheck from TCP to HTTP (/healthz on port 8083), avoiding creating the extra dummy server (e.g., nginx) to pass the TCP health check
• Update docs to recommend the AWS Load Balancer Controller and document the legacy in-tree fallback annotations.

[adamjensenbot]

Hi @fra98. Thanks for your PR!

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[fra98]

/rebase test=true