Allow users to create their own Course and Lesson patterns, which will be displayed in the Wizard for new Courses and Lessons

[alexsanford]

We want to let our users defined by themselves some Course and Lesson patterns they can later reuse.

Patterns must be shown in the Lesson/Course Creation Wizard and also in the Patterns tab on the Inserter.

We want to leverage as much as possible of this work on existing solutions in WordPress Core. At the time of writing this, there is no solution yet – more context in the slack thread here. But basically there is an ongoing discussion on how to allow users manage patterns by their own.

Definition of done:

• A teacher can create new patterns for Lessons and Courses using the editor.
• A teacher can manage (delete/update) the patterns created by themselves.
• A teacher can choose any of their created patterns in the Wizard when creating a Lesson or a Course.
• A teacher can choose any of their created patterns in the "Patterns" tab in the Inserter sidebar.

[aaronfc]

Checking with the rest of the team what experience we want to have here.
P2 team has already a solution to managing patterns and Gutenberg has a ticket to work on something similar at some point (not in the short term).

[aaronfc]

Descoping this until a general solution for this is done in Wordpress Core.

Edit: Edited opening thread with more details and removed from Evergreen project and Course and Lesson Wizard milestone.