Allow enabling/disabling REPL code execution in the Replite directive

[agriyakhetarpal]

Description

This pull request exposes functionality added upstream via jupyterlite/jupyterlite#1547 and released in jupyterlite-core version 0.5.0.

In particular, this enables the act of enabling/disabling the code execution for the Replite directive, so it is now possible for the REPL not to load the Pyodide kernel automatically and instead wait for the user's input. It can be controlled via the replite_auto_execute option globally or via the :execute: [True/False] option on a per-directive basis as an override. This appends &execute=0 to the REPL URL if False.

It is to be noted that while we support jupyterlite-core >=0.2,<0.6 via #238, this option requires jupyterlite >= 0.5 to work, and there is no effect for versions prior to jupyterlite-core 0.5.

Closes #244

Changes made

• The addition of a replite_auto_execute global configuration option, an :execute: option for the Replite directive, and corresponding URL handling
• Both options documented for readers

Additional context

This will help us make progress on matplotlib/matplotlib#22634

[agriyakhetarpal]

Thanks for the reviews – rebasing and applying the suggested changes in a moment