Don't override sidecar tolerations

[katrogan]

TL;DR

Update sidecar task plugin to append to existing user-specified tolerations (if any).

Type

• Bug Fix
• Feature
• Plugin

Are all requirements met?

• Code completed
• Smoke tested
• Unit tests added
• Code documentation added
• Any pending items have an associated Issue

Complete description

Thank you @rstanevich for finding and reporting!

Tracking Issue

flyteorg/flyte#417

Follow-up issue

NA

[codecov-commenter]

Codecov Report

Merging #104 into master will decrease coverage by 0.01%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master     #104      +/-   ##
==========================================
- Coverage   59.76%   59.74%   -0.02%     
==========================================
  Files          95       95              
  Lines        5331     5334       +3     
==========================================
+ Hits         3186     3187       +1     
- Misses       1844     1845       +1     
- Partials      301      302       +1     

Impacted Files	Coverage Δ
go/tasks/plugins/k8s/sidecar/sidecar.go	75.72% <60.00%> (-1.28%)	⬇️

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[kumare3]

Thank you, LGTM!