cleanups & refactorings

[arturcic]

• Reviewed the public API classes/methods
• Moved Git specific classes to GitVersion.Git namespace
• Introduced IConfigurationSerializer and use the interface instead of static class
• Removed System.Text.Json from GitVersion.Core
• other cleanups.

[mergify]

Thank you @arturcic for your contribution!

[arturcic]

🎉 This issue has been resolved in version 6.0.0-rc.1 🎉
The release is available on:

• GitHub Release
• Chocolatey Package
• .Net Global Tool

Your GitReleaseManager bot 📦🚀