Add Espressif Support via espup

[HeroesLament]

Hello David and team,

I would like to contribute a working implementation of support for the Espressif SOC family of devices. Currently I have the CMakeLists.txt and Kconfig tentatively getting to the cargo build step in the west build command. But there are some things I haven't really tackled yet, like we will need to change the current toolchain to esp during an Espressif build.

Let me know if you have any initial thoughts on swapping rustup toolchains during a build flow. I would love to collaborate on the topic of Rust on Zephyr further!

[d3zd3z]

Will this work with the existing esp support within Zephyr? I think this will then mainly be an issue of selecting the right cargo and the appropriate target to run. Do you need to use a cargo that comes from the Espressif toolchain?