Keymap help/reference list for the various modules

Hey @nvimdev. First and foremost, thanks a lot for your work on this awesome plugin. I've only recently started using lspsaga extensively and I am really enjoying it.

Is your feature request related to a problem? Please describe.
However, when using modules that open floating windows (and have a bunch of keymaps) I tend to forget the default keymaps and have to constantly check the documentation. I know that I can just remap the keys, but I will probably just forget all but the most commonly feature keymaps. Also, I think the default keymaps are quite sensible, its just that I just keep forgetting most of them over time.

Describe the solution you'd like
I was wondering if it would be possible to add some sort of keymap reference list/menu similar to that offered by neogit or which-key. Perhaps a similar small list of keymaps displayed somewhere in the (floating) windows would help.

Describe alternatives you've considered
neogit also has a ? binding that shows the full keymap reference menu. An alternative could be an additional keybind (<C-?> for example) to bring up another (floating) window consisting of the keymap list/reference.

Start by reviewing the existing documentation and default keymaps for the modules that open floating windows, then compare the reference behavior offered by neogit and which-key. Done means users can open a keymap reference from those modules, with the displayed bindings covering the relevant defaults.