Add Synoptic repo prototype

This feature is needed for the synoptic support in Taranta. This feature allows to save and load synoptic configuration in the Taranta repository.

A synoptic model is very similar to a dashboard but use the SVG format instead of the Taranta widget format.

TODO:

• review the concept (same repo as dashboard or?), svg inside a string field, ...
• Change the name of the project, service, ... since it's not all about dashboard configuration
• test of the new api
• Update with unique name feature introduce in !40 (merged)