fix fallbacks in backup filter policies,
- refactor the code to start with global policies, and apply
override if exists, and document the behaviour inline according
to the design
- Ensure that unlisted cluster-scoped kinds properly fall back
to global label selectors
- unlisted namespace-scoped kinds are explicitly skipped when
evaluating policy label selectors
add test coverage for GetNamespaceFilter glob matching and ordering
Added a unit test to verify that GetNamespaceFilter correctly matches
compiled glob patterns against namespace strings, and properly honors
first-match semantics when a namespace matches multiple patterns.
Signed-off-by: Adam Zhang <adam.zhang@broadcom.com>