Check Command to check completeness of a component version graph

[mandelsoft]

## Description

The new command ocm check componentversion checks component versions in an OCM
repository to be complete. All directly or indirectly references versions must also be
available in the repository of the initially checked one.

Additionally, it checks for cycles and may be more consistency conditions in the future.

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation Update
• 🎨 Style
• 🧑‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🤖 Build
• 🔁 CI
• 📦 Chore (Release)
• ⏩ Revert

Related Tickets & Documents

• Related Issue # (issue)
• Closes # (issue)
• Fixes # (issue)

Remove if not applicable

Screenshots

Added tests?

• 👍 yes
• 🙅 no, because they aren't needed
• 🙋 no, because I need help
• Separate ticket for tests # (issue/pr)

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Added to documentation?

• 📜 README.md
• 🙅 no documentation needed

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[ikhandamirov]

@mandelsoft, please see my question in #518

[hilmarf]

A few more comments at the coding would be great to easier understand what's going on... e.g. GoDoc at function