CORE-6273 Added new tool name and loc validation.

The POST /admin/tools endpoint now returns an ERR_EXISTS message if a tool with the same name and location in the request already exists in the database.
Added a "doall" call around the "map add-new-tool" calls to force validation while still being handled inside the route's "trap" call.
CORE-6285 Updated /apps/arg-preview model schema.

Added optional 'is_public' field to /apps/arg-preview request body schema.
CORE-5525: removed some dead code from the notification agent
CORE-5525: removed entity field definitions from notification entities, and made a few more changes to clean up the notification agent and facilitate testing