Seed default ConfigAdmin entry for the JAX-RS whiteboard runtime in launch/app

org.eclipse.osgitech.rest.servlet.whiteboard's
JakartarsServletWhiteboardRuntimeComponent has
configuration-policy="require": it never activates without a matching
ConfigAdmin configuration, which means it never publishes the
JakartarsServiceRuntime service, which means
org.openhab.core.io.rest.internal.resources.RootResource (which
@references that service) stays permanently unsatisfied - so /rest
404s even though individual REST resources underneath it still
register fine.

The Karaf distribution already ships the equivalent default at
distributions/openhab/src/main/resources/userdata/etc/
JakartarsServletWhiteboardRuntimeComponent.cfg; launch/app never had
one. Since launch/app uses Felix's own file-based ConfigAdmin
(felix.cm.dir) rather than Karaf's fileinstall-watched *.cfg
directory, the equivalent has to be seeded directly in Felix's own
persistence format.

Verified end-to-end on a scratch instance: the component goes from
"no config" to "active", RootResource goes from "unsatisfied
(reference)" to "active", and /rest now returns the real REST API
root listing instead of 404.

launch/app/runtime/userdata is otherwise gitignored (per-instance
runtime state); carved out a precise exception so only this one seed
file is tracked, everything else (logs, machine-specific bundle cache
paths, etc.) stays ignored as before.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: holgerfriedrich

.gitignore

@@ -19,4 +19,8 @@ xtend-gen/
 **/.settings/org.eclipse.*
 **/src/main/history/
 
-launch/app/runtime/userdata
+launch/app/runtime/userdata/*
+!launch/app/runtime/userdata/.keep
+!launch/app/runtime/userdata/config/
+launch/app/runtime/userdata/config/*
+!launch/app/runtime/userdata/config/JakartarsServletWhiteboardRuntimeComponent.config

launch/app/runtime/userdata/config/JakartarsServletWhiteboardRuntimeComponent.config

@@ -0,0 +1,3 @@
+:org.apache.felix.configadmin.revision:=L"1"
+service.pid="JakartarsServletWhiteboardRuntimeComponent"
+jersey.context.path="/"