Insert Formatted Read Time String

## Summary

As a user, I would like to be able to easily insert a formatted read time string into a document.

## Feature Request

Add an action to the extension that when triggered inserts a string at the current cursor location in an editor window.

That string should contain the current read time as calculated by this extension.

The string should have a default formatting of `Read time: ${time} minutes` or similar, where `time` is the time as calculated by this extension.

That action should be able to be connected to a keybinding and macros.

Start by reading the extension's existing read-time calculation and its action or command registration. Trace how an editor action can target the current cursor and be exposed to keybindings and macros. Done means triggering the action inserts the default formatted read-time string at the cursor.

Written by the indexing model from the issue text.