feat(policy): add interfaces for policy plugins

[lahabana]

Rework the way policy plugins work to be able to handle policy matching in the plugin

Checklist prior to review

• Link to docs PR or issue --
• Link to UI issue or PR --
• Is the issue worked on linked? --
• The PR does not hardcode values that might break projects that depend on kuma (e.g. "kumahq" as a image registry) --
• The PR will work for both Linux and Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Unit Tests --
• E2E Tests --
• Manual Universal Tests --
• Manual Kubernetes Tests --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here?

[codecov-commenter]

Codecov Report

Merging #4909 (b274129) into master (22c157d) will increase coverage by 0.00%.
The diff coverage is 48.14%.

@@           Coverage Diff           @@
##           master    #4909   +/-   ##
=======================================
  Coverage   46.68%   46.68%           
=======================================
  Files         687      687           
  Lines       46656    46681   +25     
=======================================
+ Hits        21781    21794   +13     
- Misses      22966    22977   +11     
- Partials     1909     1910    +1     

Impacted Files	Coverage Δ
pkg/xds/server/v3/reconcile.go	70.96% <0.00%> (-2.37%)	⬇️
pkg/xds/sync/dataplane_proxy_builder.go	0.00% <0.00%> (ø)
pkg/core/xds/matched_policies.go	93.33% <100.00%> (+2.50%)	⬆️
pkg/xds/cache/once/cache.go	82.05% <0.00%> (-5.13%)	⬇️
pkg/xds/cache/once/once.go	95.00% <0.00%> (-5.00%)	⬇️
pkg/core/resources/manager/cache.go	85.71% <0.00%> (ø)
pkg/plugins/leader/postgres/leader_elector.go	89.36% <0.00%> (+6.38%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.