container related code refactor

[JasonYangShadow]

Description of the Pull Request (PR):

Unify and refactor container-related code shared between API and wwctl

This fixes or addresses the following GitHub issues:

• Fixes sub-issue of separate API and wwctl implementation code #918

Before submitting a PR, make sure you have done the following:

• Signed off on all commits (e.g., using git commit --signoff) in agreement to the DCO
• Read the documentation for contributing to Warewulf
• Added changes to the CHANGELOG if necessary
• Updated userdocs if necessary
• Based this PR against the appropriate branch (typically main)
• Added myself as a contributor to the Contributors File

[JasonYangShadow]

@anderbubble this is the first trial of unifying and extracting the common code used between wwctl and API for container-related functions. Feel free to leave comments.