[FR] Keyboard shortcut for `Copy to clipboard`

### Description

There is a `Share > Export as > copy to clipboard` functionality, I would like a shortcut for this.

My use case is that sometimes I write certain documentation in AppFlowy, and since there is no grammar or spell checking, I run it through my editors linter for certain typos/grammar. The `copy to clipboard` command is really nice for this! But if it is also a shortcut it shaves some seconds :P.


### Impact

People that use doc content in other programs.

### Additional Context

- Capacities and `orgmode` also have this feature.