Removes BackoffLimitPerIndex/MaxFailedIndexes defaults from validJobSpec
and adds tweakMaxFailedIndexes. Test cases now pass both tweaks
explicitly, matching cronjob's style — the truth table is visible at
the test case rather than hidden in the fixture.
Adds a parity test for Job (new test/declarative_validation/batch/job
directory) and a case under cronjob exercising the
spec.jobTemplate.spec.backoffLimitPerIndex path.
Move the existing declarative_validation_test.go files out of
pkg/registry/ into a top-level tree at
test/declarative_validation/<group>/<kind>/. The new location pairs
each hand-written test with the per-Kind TestMain and version-init
files emitted by validation-gen, so the coverage gate runs alongside
the equivalence checks and apiVersions no longer needs to be
hand-maintained.
