Load registries for all packages declared in app def

As a user,
When I select packages that contain contributions and save,
Studio is reloaded and contains the appropriate definitions (schemas, doctypes, operations etc).

Note: the corresponding registries should be stored in a dedicated registry (i.e. not the one used by Nuxeo CLI) and invisible for the user.

ACCEPTANCE CRITERIA
As a user,
Given that I use a TP 9.10+ and select a package that contains a contributions file
When I save:

• Studio is reloaded
• The contributions of the selected package is available (schemas, doctypes, operations etc)
• I cannot see the contributions JSON in the Studio UI

As a user,
Given that I use a TP 9.10+ and select several packages that contain a contributions file
When I save:

• Studio is reloaded
• The contributions of all the selected packages are available (schemas, doctypes, operations etc)
• I cannot see the contributions JSON in the Studio UI

As a user,
Given that I use a TP 9.10+ and remove a package that contains a contributions file from an existing list
When I save:

• Studio is reloaded
• The contributions of the removed package are not available anymore
• I cannot see the contributions JSON in the Studio UI

As a user,
Given that I already have some contributions loaded through application definition
When I export contributions coming from a private package created in Nuxeo CLI and pull the changes

• both the application definition contributions and the private package contributions are available