feat: add rp2040 support

[ayushsharma82]

Adds RP2040 support using AsyncTCP_RP2040W library.

Compiles fine but I'll do some actual tests soon.

[mathieucarbou]

Thanks, reviewed, all fine.
Could you please also update the pio file and CI file ?
I'll merge after.

[mathieucarbou]

@ayushsharma82 so I am able to make it compile, there were also some errors due to the HTTP method enums. I've also updated the CI go through the pio file for pio and added a section for the rp2040.

I've set this PR to draft until you can correctly test it.

[mathieucarbou]

@ayushsharma82 : FYI I am changing the base branch to dev and will merge this PR to the dev branch.
You will be able to point to https://github.com/mathieucarbou/ESPAsyncWebServer#dev in your projects to test that.
Thanks!

[MicSG-dev]

with the Raspberry Pi pico board (RP2040) without WiFi, but using the W5500 ethernet chip, it gives the following error: c:\Users\Michel\Documents\Arduino\libraries\AsyncTCP_RP2040W\src/AsyncTCP_RP2040W.h:73:4: error : #error For RASPBERRY_PI_PICO_W board using CYW43439 WiFi only 73 | #error For RASPBERRY_PI_PICO_W board using CYW43439 WiFi only | ^~~~~

[mathieucarbou]

@MicSG-dev : please open a new issue with your pio config (board, platfrom, etc).
From memory, there were a constraint for RPI boards regarding their support.