Make upload-csvs more discoverable by adding a link to Datasette's top level nav

[obra]

It'd be lovely to not have to remember the path /-/upload-csvs, but to have somewhere in the app's UI that shows a way to navigate there if the plugin is enabled and available.

[simonw]

Definitely need to do this. It's currently blocked on a plugin hook mechanism for supporting this: simonw/datasette#690

[simonw]

Blocked awaiting simonw/datasette#1064

[simonw]

Add this to the Datasette documentation for the menu_links plugin hook once this plugin has been upgraded:

Example: `datasette-upload-csvs <https://github.com/simonw/datasette-upload-csvs>`_

[simonw]

Datasette 0.51 is out, so this is unblocked.