Add an example about replacing a core plugin

[jtpio]

Problem

In some cases, extension authors want to replace some of the default JupyterLab components with their own.

There are already some details about this in the docs: https://jupyterlab.readthedocs.io/en/stable/extension/extension_dev.html#disabledextensions

But it would be nice to have a concrete example here to illustrate that too.

Proposed Solution

Maybe that example could be about replacing the Jupyter logo in the top left corner by something else:

Since the logo is added as a plugin here:

https://github.com/jupyterlab/jupyterlab/blob/d6c3857ac6ff27811f49fd63fcd529b763024f1f/packages/application-extension/src/index.tsx#L956-L972

Additional context

Originally discussed in jupyterlab/jupyterlab#10137

[jtpio]

An example with the jlab-enhanced-launcher third-party extension replacing @jupyterlab/launcher-extension:

https://github.com/jupyterlab-contrib/jlab-enhanced-launcher/blob/49eeb7e0e0458fabbaa6197b3e673bec6c0e20ac/package.json#L83-L85

[echarles]

This would deactivate a complete extension, not a plugin within that extension, which is what we need. Is my understanding correct?

[fcollonval]

This would deactivate a complete extension, not a plugin within that extension, which is what we need. Is my understanding correct?

Indeed to deactivate only one plugin the string to set as disabledextensions should be '@jupyterlab/launcher-extension:plugin'

In the specific case of the launcher, this does not make any difference as the extension package is only providing one plugin.