[Keymap] Adding keymaps for Niu Mini and BDN9 (#7299)

[Keymap] Adding keymaps for Niu Mini and BDN9 (#7299)

* niu-mini

* fix

* media controls were off by one

* Adding some function keys

* bdn9 and some other stuff

* Fixed mouse functions on bdn9 -- the acceleration related macros are NOT optional

* ported over foo to codecoffeecode niu_mini keymap

* removing foobar

* removing foobar, moving config changes to my folder only

* limiting rule changes to my folder

* Simplifying config.h and rules.mk

* not really sure why this didn't commit the first time but...

* Fixed up the Niu Mini

* Update keyboards/keebio/bdn9/keymaps/codecoffeecode/config.h

Adding missed #pragma once to the top of my config.h for bdn9

Co-Authored-By: James Young <18669334+noroadsleft@users.noreply.github.com>
* Switching from SEND_STRING() to tap_code16

* Simplifying -> didn't need macros for Ctrl+(Home|End)