feat(raspberry-pi-os): Add Raspberry Pi OS support

[paulober]

This commit adds support for the Raspberry Pi OS debian based distribution. It includes a distro definition, 3 modules and integration into other systems like config generation and docs.

• I have signed the CLA: https://ubuntu.com/legal/contributors
• I have added my Github username to tools/.github-cla-signers
• I have included a comprehensive commit message using the guide below
• I have added unit tests to cover the new behavior under tests/unittests/
  • Test files should map to source files i.e. a source file cloudinit/example.py should be tested by tests/unittests/test_example.py
  • Run unit tests with tox -e py3
• I have kept the change small, avoiding unnecessary whitespace or non-functional changes.
• I have added a reference to issues that this PR relates to in the PR message
• I have updated the documentation with the changed behavior.
  • If the change doesn't change the user interface and is trivial, this step may be skipped.
  • Cloud-config documentation is generated from the jsonschema.
  • Generate docs with tox -e doc.

Proposed Commit Message

<type>(raspberry-pi-os): <summary>  Add support for Raspberry Pi OS

This commit adds support for the Raspberry Pi OS distro.
It includes a distro integration and detection including
three additional configuration modules:
- cc_rpi_userdata
- cc_rpi_interfaces
- cc_rpi_connect

Additional Context

It currently includes the cc_rpi_userdata module for renaming the image user and handling the setup wizard.
Maybe adding the user configuration stuff to a custom add_user implementation for the first user added
is a better approach here.

Also it would be great if the final_message would support commands. This would give use the option to remove the rc.local approach and print the IPs through the cloud-init system configuration.

@tdewey-rpi, @XECDesign, @ghollingworth, @will-v-pi

Test Steps

Tested with custom Raspberry Pi OS image.
Will add more

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[paulober]

Is there an option if a setting for rpi_interfaces has been set, to tell the power_state_change module that a reboot is required?

[tdewey-rpi]

Some additional context:

This PR (and the linked GitHub PRs from other repos) are part of a wider desire to move to using cloud-init as the customisation scheme for Raspberry Pi OS, with associated infrastructure in Raspberry Pi Imager to ensure we maintain feature parity (if not an increased feature set) with the current 'firstrun' style customisation scheme.

Going forward, assuming this PR is merged and our migration proceeds along happily enough, my plan is to recommend to each distro vendor supplying OS images to the Raspberry Pi Imager that they also adopt cloud-init as their customisation scheme. This may result in additional PRs adding distro features to cloud-init in a similar manner to this PR - but should absolutely improve the experience for end users across the board.

[holmanb]

Upstream dhclient is abandoned. Is raspberry-pi-os's plan to support it forever?

[tdewey-rpi]

This was included as an error, and dhclient is not actually used by Raspberry Pi OS - instead, we use network-manager's built in DHCP client. I believe this has been corrected in the latest version of this PR.

[holmanb]

Which of these does raspberry-pi-os support and plan to use?