[🚀 | Feature request]: Display app shortcuts

[mmmarcos]

What you would like to accomplish

App shortcuts allow to improve user experience, we should document them in the User Guide. Also it would be useful to have them actually displayed somewhere in the app.

How the feature should work

This could be done via an entry in the main menu App shortcuts or with a (?) icon somewhere in each page.

That could show a dialog displaying shortcuts, probably grouped by category (general shortcuts, file/folder shortcuts, etc.) or at least open the documentation at the right page (depends on #9007)

@Ironicbay suggests to also display shortcuts on each action tooltip (e.g. <Ctrl>+G on hover on Grid/List button).

Where are the shortcuts defined?

The issue #6183 displays the list of shortcuts to be implemented, but not all of them have been implemented. We should check if that list is up to date with the current code (i.e. search for "hotkeys.add" or "defineShortcuts" in .vue files). Or, as a quick hack we could add an export function to hotkeyManager.ts.

[mmmarcos]

Example: Slack displays a link to the user docs https://slack.com/help/articles/201374536-Slack-keyboard-shortcuts

[mmmarcos]

Example: Spotify shows a popup dialog with a list of common shortcuts