Add support for generating embassy/async projects

[MabezDev]

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We should probably add an embassy_main macro for Xtensa to make this easier.

[ctron]

I would love to have an example/template with async, embassy, and esp.

[MabezDev]

We have plenty of async examples in esp-hal, and esp-wifi. As well as some projects in awesome-esp-rust. Would be nice to support generation here though, but it gets a bit tricky with the number of options we have.

[ctron]

We have plenty of async examples in esp-hal, and esp-wifi.

I was struggling a bit with the different options, compilation issues (around atomic-polyfil, portable-atomic, newer embassy versions, …). It took me a while, but in the end I got something going (with esp-hal from main branch). However, none of the examples seemed to work for me (due to various reasons).

I think it would be good to have a standalone example, which can be tested on a regular basis. And just forked/cloned to get started. And that feels pretty close to this repository.

[MabezDev]

Yeah, we're going through a bit of churn at the moment due to some atomic changes, we're making a clean break and moving solely to portable atomic, but this will cause some issues when running mixed versions of git and old releases. We hope to have a release from esp-hal and esp-wifi soon to sort this.