Switch publishing to maven central

[Simply007]

Motivation

Which issue does this fix? Fixes #130

Checklist

• Code follows coding conventions held in this repo
• Automated tests have been added
• Tests are passing
• Docs have been updated (if applicable)
• Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

How to test

If manual testing is required, what are the steps?

[Simply007]

TODO:

• describe release process - https://github.com/Kentico/kontent-java-packages/wiki/Release-process
• test sample apps with snapshots
• stage new version
• release the version - https://repo1.maven.org/maven2/com/github/kentico/kontent-delivery/ + https://repo1.maven.org/maven2/com/github/kentico/kontent-delivery-generators/

[Simply007]

Release note: https://app.kontent.ai/ad858591-7c5b-00e9-52c1-796f3aebc535/content-inventory/00000000-0000-0000-0000-000000000000/content/ba6fabfc-d3f9-426a-8f6f-c98c381d51e4

[petrsvihlik]

I also adjusted the - https://github.com/Kentico/kontent-java-packages/wiki/Release-process

• you might want to check it.

[Simply007]

• - redo the diagram on https://github.com/Kentico/kontent-java-packages/wiki/Release-process

Already re-reviewed by @makma