[next] Add test cases for route /index handling

[ijjk]

This adds some test cases for /index handling to ensure we are being consistent with local development and production

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@dce9a89). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #4002   +/-   ##
=========================================
  Coverage          ?   13.57%           
=========================================
  Files             ?      278           
  Lines             ?     9971           
  Branches          ?     1301           
=========================================
  Hits              ?     1354           
  Misses            ?     8524           
  Partials          ?       93           

Impacted Files	Coverage Δ
src/util/prompt-options.js	0.00% <0.00%> (ø)
src/util/get-dist-tag.ts	77.77% <0.00%> (ø)
src/commands/projects.js	0.00% <0.00%> (ø)
src/util/domains/move-out-domain.ts	0.00% <0.00%> (ø)
src/util/domains/check-transfer.ts	0.00% <0.00%> (ø)
src/commands/domains/ls.ts	0.00% <0.00%> (ø)
src/commands/login.js	0.00% <0.00%> (ø)
src/util/get-scope.ts	0.00% <0.00%> (ø)
src/util/is-valid-name.ts	80.00% <0.00%> (ø)
src/util/scale/region-or-dc-to-dc.js	0.00% <0.00%> (ø)
... and 268 more

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