DAL/Node: `get_proto_parameters` returns the most recent parameters

What

By default Node_context.get_proto_parameters returns the most recent parameters, which are those for the latest finalized head.

On top of !16623 (merged) and !16616 (merged).

Addresses one item from #7741 (closed).

Why

It previously returned the parameters known at start-up, while usually what is needed are the most recent ones.

How

Get them at the same time a new plugin is added, that is, when a protocol migration occurs. Also store them together with plugins.