feat(spark): migrate from kuttl to chainsaw

[razvan]

Description

As decided in the testing kick-off meeting from 15 Oct 2025.

Migrate the Spark integration tests from kuttl to chainsaw and evaluate the result.

Acceptance

• There is set of chainsaw tests (alongside the existing kuttl tests) that cover the same (or more!) cases.
• There is a document (or comment here) that clearly describes the relevant differences between the two.
  It is especially important to address the following points:
  • how test dimensions can be grouped together (value binding, templating)
  • summary report and especially error highlighting
  • manifest file reuse across test cases
  • the possibility to retry failed test (steps)