Allow using/setting different keyboard mappings for keyboard input

[kennethso168]

This is a continuation of the discussion on #9

There are two ways of doing this:

1. The user sets the keymap when running the build script, only that keymap will be put into the preboot image and the image will be configured to use that keymap only.
2. Put all keymaps into the preboot image and allow user to select a keymap at runtime

The kmaps.tcz package is only 140.0K large so I think the first way should be viable (and it is better as it allows the user to enter the correct password even if he doesn't have the correct keyboard on hand). And for this we need to think of a way to let user change the keymap at runtime.

We can make reference to SystemRescueCD's way to letting user change the keymap:

https://github.com/Jip-Hop/sedunlocksrv-pba/assets/5262487/47df98fd-1422-4564-b406-86250a29a651

SystemRescueCD implements this using the dialog binary. I have tried rebuilding the image while adding kmaps.tcz and dialog.tcz. The resultant image is the same size as before.