[FEATURE] Add OS-default keyboard shortcuts for copy/paste in TabnineChat

[pgib]

Is your feature request related to a problem? Please describe.

Copying from and pasting to the system clipboard is only available via the contextual menu. I should be able to use Command-c/Command-v (Mac) or Ctrl-c/Ctrl-v (Windows/Linux) to access these functions like any other app would allow.

Describe the solution you'd like

Add default shortcut keys to these basic, system-level functions.

Describe alternatives you've considered

N/A

Additional context