Fix remote sidecar url

[jeefy]

Fixes #3957

URL structure is not the same between Heapster and Sidecar, so that was an artifact.

Props to @kadenlnelson for finding the problem :)

[k8s-ci-robot]

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This pull-request has been approved by: jeefy

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[ghost]

As long as it's been tested, LGTM

[codecov]

Codecov Report

Merging #3960 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3960      +/-   ##
==========================================
- Coverage   47.29%   47.28%   -0.02%     
==========================================
  Files         182      182              
  Lines        8403     8403              
  Branches       72       72              
==========================================
- Hits         3974     3973       -1     
- Misses       4184     4185       +1     
  Partials      245      245

Impacted Files	Coverage Δ
...c/app/backend/integration/metric/sidecar/client.go	72% <100%> (ø)	⬆️
...p/backend/integration/metric/common/aggregation.go	89.09% <0%> (-1.82%)	⬇️

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