[FLINK-36145] Rename flinkStateSnapshotReference to initialState

[gyfora]

What is the purpose of the change

Rename JobSpec.flinkStateSnapshotReference to JobSpec.initialState. This should make less verbose and easier to memorize for users.

flinkStateSnapshotReference field has not been released officially yet, so this change should not affect production users.

Brief change log

• Rename in Java, Markdown files and examples
• Regenerate CRDs

Verifying this change

• Unit tests

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

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? updated

[gyfora]

Actually @tweise @mateczagany , I have a slight concern about this initialState reference field overall. It may make sense to simply keep the current initialSavepointPath field, because having a reference like field may allow users to "steal" the savepointpath of other users through the operator's permissions.

With the old way you either know the path or you don't.