Allow users to opt-out from Nimbus rollouts

[tarikeshaq]

Fixes https://mozilla-hub.atlassian.net/browse/EXP-2156

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[codecov-commenter]

Codecov Report

Merging #4807 (a269366) into main (2e88010) will decrease coverage by 0.00%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main    #4807      +/-   ##
==========================================
- Coverage   81.49%   81.48%   -0.01%     
==========================================
  Files          49       49              
  Lines        5653     5656       +3     
==========================================
+ Hits         4607     4609       +2     
- Misses       1046     1047       +1     

Impacted Files	Coverage Δ
components/nimbus/src/enrollment.rs	96.96% <80.00%> (-0.05%)	⬇️

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[jhugman]

Is this what we want? ISTR we decided we didn't want to opt out of rollouts (just experiments/studies).

[tarikeshaq]

Is this what we want? ISTR we decided we didn't want to opt out of rollouts (just experiments/studies).

@jhugman yeah, confirmed on slack with Jared when the bug was filed

[jhugman]

Ship it!