Flip the PMS5003 uart pins on AG Basic

[jvdstoel-home]

Some Airgradient models come with the RX and TX UART pins for the PMS5003 swapped. Example: https://www.airgradient.com/documentation/diy-outdoor/ has them flipped compared to the one currently configured in this repository (example: https://www.airgradient.com/documentation/diy-pro-v42/).

This PR adds a way to configure this flipping and enables it for the basic model.

[MallocArray]

This is the first I've heard of the DIY Outdoor model, which isn't a very popular or well known option. It appears that if anything, this case of the flipped pins only applies to that DIY Outdoor as the regular Basic board that I have is correct with this config:
https://www.airgradient.com/documentation/diy/

There is a higher version number of this board https://www.airgradient.com/documentation/diy-v4/ but I'm not sure if that also flipped the pins. If we discover that this revision of the board for the indoor model did indeed flip the pins, then I'll be in favor of adding support to more easily switch this around.

If the flipped pins only applies to the DIY Outdoor model, then I would probably go for a note about how to use the !extends feature to override those two lines without changing the main package.

I don't even see the DIY Outdoor listed on their page with supposedly all models:
https://www.airgradient.com/documentation/ag-models/

[jvdstoel-home]

For me finding the correct documentation was a huge mess. But it is the AirGradient Open Air (Generation 1). With status: Actively Maintained... I bought the kit from a local webshop in October last year.... I really don't know how popular each model is.