Refactor code and increase test coverage

[odubajDT]

Pre-requisites:

• Introduce v1beta1 API version #529
• [FEATURE] Support v1beta1 API of OFO flagd#983
• Use of v1beta1 in OFO logic #531

Goal

Clean up logic of packages in OFO

Details

There are multiple possibilities to improve the maintability of OFO logic, especially we are talking about the following:

• polish controller logic; increase unit tests coverage
• polish flagdproxy handler
• polish flagdinjector
• create global common package and move controllers/common into it
• move pkg into global common package
• polish and increase coverage of common package
• polish and increase coverage of webhook package -> some functions can be moved to a local webhooks/common package for better readibility
• remove all nolint comments (where it makes sense)

DoD

• code is better structured and easier to read/understand
• test coverage is increased in webhook and common packages

Notes

Some of the adjustments can be found in the PoC