[Improvement][docs]: Automate building document from mdbook

[sikiryl]

Pipeline Improvement

• Track state of mdbook folder (if someone change somethings in this folder)
• Automate Github Action to use mdbook build -d ../docs for building markup document to levis page

[aaronamm]

@sikiryl please confirm if I understand the requirements correctly. Then I will create a PR for this issue.

• Create a new GitHub Actions workflow.

• In the workflow file

  • Trigged whenever, there is a new push the main branch.
  • Pull the latest source code
  • Build document with mdbook command to GitHub page branch that you have configured, please let me know a branch name.e.g. ghpage.

  Thanks.

[aaronamm]

@sikiryl This issue is in process by this PR.
https://github.com/kubeopsskills/levis/pull/14/files#diff-660c65eb3efc05d4f21ef1bf94097c800e4d43a155309278ad74409257d5ef4aR1