Feature: save active blueprint as default

[abey79]

Currently, the only means to set a blueprint as default are:

• using the logging SDK
• loading a blueprint from file

Specifically, if you want to set whatever current blueprint you have as default (e.g. because you want to mess with it and easily revert to it), you must:

• save the blueprint somewhere
• load it back
  ...which is cumbersome.

We should have a "Save active blueprint as default" feature. Relatedly, we should also persist default blueprint just like we do for active blueprints, so that this sequence of action yields to the expected result:

• mess with blueprint
• save as default
• further mess with blueprint
• quit viewer
• launch viewer
• reload the same recording
• => both the active and default blueprint are in the same state as they were upon quitting the viewer

Related:

• "Which is the active blueprint?" tracking issues #5670
• Allow user to switch between "app blueprint" and "recording blueprint" #5640
• Determine and indicate to user when "Reset Blueprint" button will do something valuable #5692