linux-postmarketos-mediatek-mt8183: add kconfigcheck-community

Not tested because I do not have a device, but it should be fine if our kconfig checks are accurate

I am not sure it is relevant to have pmb:kconfigcheck-community for kernels in testing, but it is convenient to cover all needed features this way and the long-term goal is to move this to community anyway, so this is a step forward

Also, update CODEOWNERS and maintainerships for this

CC @binarycraft