Add ESP32 support (backport #680)

[mergify]

This is an automatic backport of pull request #680 done by Mergify.
Cherry-pick of a809407 has failed:

On branch mergify/bp/main/pr-680
Your branch is up to date with 'origin/main'.

You are currently cherry-picking commit a809407.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .github/workflows/ci.yml
	modified:   README.md
	modified:   examples/micro-ros_publisher_wifi/micro-ros_publisher_wifi.ino
	new file:   extras/library_generation/esp32_toolchain.cmake
	modified:   library.properties
	modified:   src/micro_ros_arduino.h
	modified:   src/wifi_transport.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   built_packages
	both modified:   extras/library_generation/library_generation.sh

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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