add CI workflow to crosscompile all the tools and pubblish them

[umbynos]

I've created the workflow to cross-compile all the tools (picotool, elf2uf2. and rp2040load). ⚒️
The workflow is divided in:

• a job which uses a docker container (called crossbuild) with all the toolchains inside required to cross-compile the two tools from raspberry pi. The binaries produced are as static and self-contained as possible. (Obviously, this is run in parallel to minimize time) 🏃
• a job that cross-compiles the go tool called rp2040load, cross-compiling this tool is so much easier than compiling the C++ ones. 😅
• one last job used to move in the correct folders the binaries and to tar.bz2 them and upload them in the release page and on s3 download server 🆙
  
  
  In less than 6 5 mins we can produce a release! 📦 🥳
  Release binaries are structured as follows:

release/
├── tools_darwin_amd64
│   ├── elf2uf2
│   ├── picotool
│   └── rp2040load
├── tools_linux_386
│   ├── elf2uf2
│   ├── picotool
│   └── rp2040load
├── tools_linux_amd64
│   ├── elf2uf2
│   ├── picotool
│   └── rp2040load
├── tools_linux_arm
│   ├── elf2uf2
│   ├── picotool
│   └── rp2040load
├── tools_linux_arm64
│   ├── elf2uf2
│   ├── picotool
│   └── rp2040load
└── tools_windows_386
    ├── elf2uf2.exe
    ├── picotool.exe
    └── rp2040load.exe

TODO:

• Clean up the container as of now it weights almost 10gb (and maybe move it to another repo)
• Clean up the repo (removing old and useless scripts)
• Publish artifacts on download servers
• Patches probably can be removed and added as command-line flags

[umbynos]

With the optimization from #2, i managed to drop the image size from 9.22GB to 7.76GB and thus cut CI step downloading the container from 4mins to 3 🥳 🎈

[umbynos]

apparently aws cli does not give a meaningful message when credentials or bucket are wrong.. The error message was:

fatal error: An error occurred (SignatureDoesNotMatch) when calling the ListObjectsV2 operation: The request signature we calculated does not match the signature you provided. Check your key and signing method.

Reinserting the secrets solved the problem. Thanks @rsora for the help in the troubleshooting

[umbynos]

I know it's not ideal, but IMHO it's better than duplicating the steps, like it were in the beginning.
I tried some tinkering to have the cmake flags as variables but I think it was losing readability..

[per1234]

Great work Umberto!