feat: create a bootc module

[p5]

Proposed Commit Message

feat(bootc): create a bootc module

Provides users of bootc systems (such as RHEL Image Mode) with a way
to switch onto their desired target image during the initialisation 
process.

Additional Context

I'll be discussing this with the folks over at RedHat to see if this is something they would be interested in.

Here's how a user would use it:

#cloud-config

bootc:
  image: quay.io/myorg/my-image:latest

Test Steps

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>)