Split trusted/untrusted across all nodes, rather than within a region

[thomshutt]

What does this pull request do? Explain your changes. (required)

Follow-on PR from #1064. That PR marks 50% of Os within a region as untrusted, but the actual desired behaviour was an overall 50/50 split.

Specific updates (required)

-

How did you test each of these updates (required)

Deployed to Staging and hit the /region API endpoint to test

Does this pull request close any open issues?

Screenshots (optional):

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

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[codecov]

Codecov Report

Merging #1083 (5b0d3c8) into master (ca0b25f) will increase coverage by 0.01337%.
The diff coverage is 100.00000%.

@@                 Coverage Diff                 @@
##              master       #1083         +/-   ##
===================================================
+ Coverage   46.14048%   46.15385%   +0.01337%     
===================================================
  Files             64          64                 
  Lines           4029        4030          +1     
  Branches         679         679                 
===================================================
+ Hits            1859        1860          +1     
  Misses          1971        1971                 
  Partials         199         199                 

Impacted Files	Coverage Δ
packages/api/src/controllers/region.js	75.00000% <100.00000%> (+0.92592%)	⬆️

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[victorges]

lgtm