Improve Namespace-awareness for CRDs

[eloyekunle]

• On the backend, only filter CRDs by namespace if namespace-scoped.
• On the frontend, adds a new page for cluster-scoped CRD objects.

[codecov]

Codecov Report

Merging #4189 into master will increase coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #4189      +/-   ##
==========================================
+ Coverage   46.33%   46.34%   +0.01%     
==========================================
  Files         198      198              
  Lines        9159     9159              
  Branches      105      105              
==========================================
+ Hits         4244     4245       +1     
+ Misses       4656     4655       -1     
  Partials      259      259

Impacted Files	Coverage Δ
...ckend/resource/customresourcedefinition/objects.go	0% <0%> (ø)	⬆️
...p/backend/integration/metric/common/aggregation.go	90.9% <0%> (+1.81%)	⬆️

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[maciaszczykm]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: eloyekunle, maciaszczykm

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