Add CI for individual ROS distro branches (#15)

[atticusrussell]

Integrates Humble branch with CI from #45:

• individual workflows per supported ROS distro
• made PlatformIO firmware CI reusable and callable from other workflows
• firmware build status badges on README for each branch
• CI actions run nightly to test for broken dependencies

[grassjelly]

Hey @atticusrussell . Thanks for the PR. I added a comment on the README file.