Add `--keybindings` option to show keybindings

[simjnd]

Is your feature request related to a problem? Please describe. Use gum pager: It shows keybindings at the bottom. Use any other component : No keybindings are shown.

Describe the solution you'd like Since some keybindings may not be obvious (You need TAB to toggle selection in gum filter but SPACE in gum choose, g and G are shortcuts to go to the top or bottom of the list, you can use the right / left arrow keys in gum file, etc.) it would be interesting to add an option (e.g. --keybindings) to optionally display these keybindings at the bottom of the input to make it more accessible for users not used to CLIs.

[maaslalani]

👍 I think we can introduce a flag called --show-help or --hide-help to show/remove them.