Add the ability to inject variables in the "Http Request" action in scenes

[Pierre-Gilles]

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• If your changes affects code, did your write the tests?
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Description of change

Please provide a description of the change here. It's always best with screenshots, so don't hesitate to add some!

[relativeci]

Job #325: Bundle Size — 6.74MB (+0.04%).

ee5b284 vs b6c5393

Changed metrics (3/10)

Metric	Current	Baseline
Initial JS	2.87MB(+0.09%)	2.86MB
Cache Invalidation	42.37%	0%
Modules	1172(+0.09%)	1171

Changed assets by type (1/7)

	Current	Baseline
JS	4.85MB (+0.05%)	4.85MB

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View Job #325 report on app.relative-ci.com

[codecov]

Codecov Report

Merging #1540 (4781c49) into master (cb444cc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1540   +/-   ##
=======================================
  Coverage   96.59%   96.59%           
=======================================
  Files         627      627           
  Lines        9159     9159           
=======================================
  Hits         8847     8847           
  Misses        312      312           

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Continue to review full report at Codecov.

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