display shortcuts on hover

**Is your suggestion related to a problem? Please describe.**
I don't think it's very intuitive to discover shortcuts to actions I do often.

**Describe the solution you'd like**
E.g. there is a shortcut for uploading a file (Ctrl+Shift+U). When I hover over the upload button/paper clip it would be nice if there'd be a hover text like "Upload file (Ctrl+Shift+U)".

Currently the only way to discover that shortcut is actively opening the shortcut overview on Ctrl+/ and have a look if there is a shortcut for uploads.

**Describe alternatives you've considered**
The alternative solution is the manual lookup, but imo it's very hard to parse that overview and it'll get even harder when/if Riot gets more shortcuts over time.

**Additional context**