[FLINK-38147] Add Flink 2.1 support

[gyfora]

Brief change log

• Add Flink 2.1.0 version support
• Update CI matrix

Verifying this change

E2s already should cover it

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changes to the CustomResourceDescriptors: yes
• Core observer or reconciler logic that is regularly executed: no