[FLINK-37236] Flink 2.0 preview support

[gyfora]

What is the purpose of the change

This PR adds support for the 2.0 preview release of Flink. As a necessary prerequisite it also includes a bumping of the operator Flink dependency to 1.20.

The major incompatibility that was addressed here is related to the YAML config handling. Flink 2.0 only supports the new standardized yaml runtime config while 1.20 and older versions supported both the old and the new.

The operator previously only used the legacy flat yaml config. Now a new logic has been put in place for Flink 2.0 and above to automatically convert and use the new yaml configs.

Brief change log

• Bump Flink dependency to 1.20
• Update examples to 1.20
• Update NOTICE Files
• Update e2e version matrix to include 2.0
• Introduce custom FlinkConfMountDecorator to support standard yaml configs

Verifying this change

• Existing e2es,
• [TODO] unit tests for FlinkConfMountDecorator

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): yes
• The public API, i.e., is any changes to the CustomResourceDescriptors: yes
• Core observer or reconciler logic that is regularly executed: yes

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? JavaDocs

[1996fanrui]

LGTM assuming all tests are green.