feat: add secret requirement contract to dynamic parameters (#24785)

Adds structured `secret_requirements` to dynamic parameter responses and
enforces missing required secrets during workspace start.

Stop, delete, and tag rendering paths skip secret requirement
enforcement so unmet secrets do not prevent cleanup. The SDK, generated
API docs/types, and backend render/resolver/wsbuilder tests are updated
for the new contract.

coderd/testdata/parameters/secret_required/main.tf

@@ -0,0 +1,12 @@
+terraform {
+  required_providers {
+    coder = {
+      source = "coder/coder"
+    }
+  }
+}
+
+data "coder_secret" "gh" {
+  env          = "GITHUB_TOKEN"
+  help_message = "Add a GitHub PAT with env=GITHUB_TOKEN"
+}