feat: add Gateway API support (#1073)

Add full Gateway API support for exposing Gitea via HTTPRoute, TCPRoute, BackendTLSPolicy, and ClientSettingsPolicy resources.

New templates:
- `httpRoute.yaml` — renders an HTTPRoute with configurable
  parentRefs, hostnames, and rules (defaults to PathPrefix `/`)
- `tcpRoute.yaml` — renders a TCPRoute for SSH traffic
- `backendTLSPolicy.yaml` — renders a BackendTLSPolicy for
  encrypted backend connections with required validation config
- `clientSettingsPolicy.yaml` — renders an NGINX Gateway Fabric
  ClientSettingsPolicy to raise the request body size limit

Infrastructure:
- `gatewayAPI.enabled` global toggle gates all resources
- Resources grouped under `gatewayAPI.core.*` and `gatewayAPI.nginx.*`
- Helper templates extracted into dedicated `_*.tpl` files
- Service name helpers (`gitea.service.http.name`, `gitea.service.ssh.name`)
  extracted into `_services.tpl`; service templates renamed to camelCase
- `ROOT_URL`, `DOMAIN`, and `SSH_DOMAIN` auto-resolve from
  `httpRoute.hostnames[0]`; `httpRoute.tls` switches to `https`

Documentation:
- New `docs/gateway-api.md` with topology examples, BackendTLSPolicy
  setup, sectionName guidance, SSH considerations, and NGINX body
  size limit configuration
- `.github/copilot-instructions.md` with project conventions
- README parameter table auto-generated via `make readme`

Tests:
- Helm unit tests for all four new resource templates
- Config tests for hostname/TLS resolution from Gateway API values

Co-authored-by: Todd Marimon <toddmarimon@gmail.com>

unittests/helm/deployment/svc-configuration.yaml

@@ -1,13 +1,13 @@
-suite: ssh-svc / http-svc template (Services configuration)
+suite: sshService / httpService template (Services configuration)
 release:
   name: gitea-unittests
   namespace: testing
 templates:
-  - templates/gitea/ssh-svc.yaml
-  - templates/gitea/http-svc.yaml
+  - templates/gitea/sshService.yaml
+  - templates/gitea/httpService.yaml
 tests:
-  - it: supports adding custom labels to ssh-svc
-    template: templates/gitea/ssh-svc.yaml
+  - it: supports adding custom labels to sshService
+    template: templates/gitea/sshService.yaml
     set:
       service:
         ssh:
@@ -19,7 +19,7 @@ tests:
           value: "testvalue"
 
   - it: keeps existing labels (ssh)
-    template: templates/gitea/ssh-svc.yaml
+    template: templates/gitea/sshService.yaml
     set:
       service:
         ssh:
@@ -28,8 +28,8 @@ tests:
       - exists:
           path: metadata.labels["app"]
 
-  - it: supports adding custom labels to http-svc
-    template: templates/gitea/http-svc.yaml
+  - it: supports adding custom labels to httpService
+    template: templates/gitea/httpService.yaml
     set:
       service:
         http:
@@ -41,7 +41,7 @@ tests:
           value: "testvalue"
 
   - it: keeps existing labels (http)
-    template: templates/gitea/http-svc.yaml
+    template: templates/gitea/httpService.yaml
     set:
       service:
         http:
@@ -51,7 +51,7 @@ tests:
           path: metadata.labels["app"]
 
   - it: render service.ssh.loadBalancerClass if set and type is LoadBalancer
-    template: templates/gitea/ssh-svc.yaml
+    template: templates/gitea/sshService.yaml
     set:
       service:
         ssh:
@@ -73,7 +73,7 @@ tests:
           value: ["1.2.3.4/32", "5.6.7.8/32"]
 
   - it: does not render when loadbalancer properties are set but type is not loadBalancerClass
-    template: templates/gitea/http-svc.yaml
+    template: templates/gitea/httpService.yaml
     set:
       service:
         http:
@@ -92,7 +92,7 @@ tests:
           path: spec.loadBalancerSourceRanges
 
   - it: does not render loadBalancerClass by default even when type is LoadBalancer
-    template: templates/gitea/http-svc.yaml
+    template: templates/gitea/httpService.yaml
     set:
       service:
         http:
@@ -107,8 +107,8 @@ tests:
 
   - it: both ssh and http services exist
     templates:
-      - templates/gitea/ssh-svc.yaml
-      - templates/gitea/http-svc.yaml
+      - templates/gitea/sshService.yaml
+      - templates/gitea/httpService.yaml
     asserts:
       - matchRegex:
           path: metadata.name