fix(eas-cli): avoid adding expo.extra data from config plugins in eas init

[byCedric]

Why

This fixes the eas init command, where we currently merge the expo.extra data in the manifest with plugin-generated data. You can repro this through the steps defined in the test plan.

Note that in the newer @expo/config package, modifying now also merges existing properties. Once thats released, we can use that instead of manually merging this data.

See: expo/expo#30782, expo/expo#30783

How

• Disable the plugins modification on the loaded expo config
• (Still) manually merge the expo.extra object with expo.extra.eas.projectId

Test Plan

• $ bun create expo ./test-eas-init
• $ cd ./test-eas-init
• Check app.json, ensure it does NOT have expo.extra but does have expo.plugins[expo-router]
• $ eas init
• Check app.json's expo.extra only contains expo.extra.eas.projectId, and nothing from the router plugin

[github-actions]

✅ Thank you for adding the changelog entry!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.27%. Comparing base (12efaf1) to head (f01133d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2554      +/-   ##
==========================================
+ Coverage   52.27%   52.27%   +0.01%     
==========================================
  Files         557      557              
  Lines       20989    20990       +1     
  Branches     4283     4284       +1     
==========================================
+ Hits        10969    10970       +1     
  Misses       9158     9158              
  Partials      862      862              

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[github-actions]

Size Change: -1.58 kB (0%)

Total Size: 52.9 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	52.9 MB	-1.58 kB (0%)

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