Introduces application-scoped policies and global auto-applied policies
for KubeVela.
Key changes:
- PolicyDefinition gains `scope`, `global`, and `priority` fields
- Global policies (global=true, scope=Application) are auto-applied to
every Application in their namespace (and vela-system globals apply
cluster-wide) without being listed in spec.policies
- PolicyScopeIndex: in-memory singleton index of PolicyDefinition
metadata, bootstrapped at startup and kept live via watch events.
Follows KubeVela's 2-step lookup (local namespace → vela-system)
- ApplicationPolicyCache: per-app cache of rendered policy results,
invalidated by spec hash, revision hash, or TTL; cleared on deletion
- Policy rendering pipeline extended to inject global policies before
user-specified ones, respecting priority ordering
- Appfile.Context carries context.Context from controller into rendering
- Feature gates: EnableApplicationScopedPolicies and EnableGlobalPolicies
(both Alpha, default false); admission webhook warns when a
PolicyDefinition targets a disabled gate
Signed-off-by: Brian Kane <briankane1@gmail.com>
