CORE-5832 Fixes for /apps/:id update labels endpoint.

Updated the route to use the ID in the URL as the App ID.
Fixes for metadactyl.persistence.app-metadata.relabel, including properly decoding and validating parameter list-item groups, no longer attempting sql updates with empty values, and no longer updating the "name" field of parameters.
Refactored metadactyl.zoidberg/get-app into metadactyl.persistence.app-metadata/get-app.
Refactored metadactyl.service.app-metadata/relabel-app to use metadactyl.zoidberg/verify-app-ownership.
CORE-5832 Refactored root "/" endpoint.

Requests to the root endpoint will now be redirected to the api documentation.
CORE-5832 Fixed typo.

The defalut curse must end...
CORE-5832 Refactored /arg-preview endpoint.

Renamed to /apps/arg-preview and added swagger docs.