major rework of backend loading and usage:

- split config from user data to config.json, add config.hson.template
- moved default user data localdb to root folder
- moved pve, localdb, ldap backend handlers to backends sub folder
- add dynamic loading of all backends
- add dynamic mapping for auth backends to support multiple auth sources
- update affected endpoints

.gitignore

@@ -1,4 +1,5 @@
 **/package-lock.json
 **/node_modules
 **/localdb.json
-**/docs
+**/docs
+**/config.json