refactor: move config_path from root into install_methods

Migrated all 80 app JSON files to place config_path inside each
install_methods object instead of at the root level. This allows
different install methods (e.g. Debian vs Alpine) to have distinct
config paths.

Also updated AGENTS.md JSON structure example to reflect the change.

json/step-ca.json

@@ -12,12 +12,12 @@
   "documentation": "https://smallstep.com/docs/step-ca/",
   "website": "https://github.com/smallstep/certificates",
   "logo": "https://cdn.jsdelivr.net/gh/selfhst/icons@main/webp/step-ca.webp",
-  "config_path": "/etc/step-ca",
   "description": "A private certificate authority (X.509 & SSH) & ACME server for secure automated certificate management, so you can use TLS everywhere & SSO for SSH.",
   "install_methods": [
     {
       "type": "default",
       "script": "ct/step-ca.sh",
+      "config_path": "/etc/step-ca",
       "resources": {
         "cpu": 1,
         "ram": 512,