Facilitate new forjj instantiation

[clarsonneur]

feature context

When a forge infrastructure is described (from an infra repo), we could run forjj on top on it, like deploying a Development forge.

But, such forge often requires some secrets to be defined before for forjj to work properly.

How forjj shoud behave?

forjj should detect if secrets has never been defined on the selected deployment.

Then forjj should ask interactively for those secrets with appropriate documentation described by each plugins and save it

forjj secrets should be able to provide the flag description or documentation and get more details with forjj secrets describe