feat: add send_named_int function and Lua binding

[ben-xD]

This is useful to send NAMED_VALUE_INT mavlink messages in the same way as NAMED_VALUE_FLOAT, including in lua scripts:

local an_integer = 1
gcs:send_named_int("EXAMPLE", an_integer)

I've confirmed this works by building Arduplane in Docker and then running it my lua script.

[Lalbabu2001]

Hi please add support for this board
https://www.6sfull.cz/en/neutronrc-mini-f405-2-6s-20--20-30--30/

Don't forget to add Bmp 280 baro because new versions come with bmp280.
Also add support for PPM .
Thanks.

[rmackay9]

Hi @Lalbabu2001, please do not spam the pull requests. That's definitely not a good way to achieve what you'd like.