Make sure that listPipelines can be called without authentication

[glatard]

So that platforms can advertise their pipelines openly.

• The platform may not return the same list if the method is authenticated or not.
• The canExecute boolean can be customized based on the rights of the (non-)authenticated user.
• Platform may return an empty list if it doesn't want to advertise its pipelines.

Agreed during meeting.

[axlbonnet]

I made that change but I'm not sure about the value of canExecute when listPipelines is used anonymously. An anonymous user cannot used the initExecution so what would that mean is a pipeline is described to be executable to an anonymous user ? That's why I wrote the canExecute must be false in my PR, as it is clear and logic.

An other solution would be to declare that a canExecute=true pipeline returned to an anonymous mean that it's a public pipeline that is accessible after registration. I would be OK for that.