[eas-cli] do not set default image

[wkozyra95]

Checklist

• I've added an entry to CHANGELOG.md if necessary.
• I've tagged the changelog entry with [EAS BUILD API] if it's a part of a breaking change to EAS Build API (only possible when updating @expo/eas-build-job package).

Why

We always specify the image field in the job object. As a result, when processing the build in the backend, we don't know whether the image was specified explicitly or by default.

How

Don't resolve the image in the CLI.

Test Plan

Tested manually.

[dsokal]

Fix type errors.

[dsokal]

... and add a changelog entry.

[github-actions]

Size Change: +320 B (0%)

Total Size: 22.5 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	22.5 MB	+320 B (0%)

_{compressed-size-action}

[codecov]

Codecov Report

Merging #675 (b3fadab) into main (e30f62e) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #675      +/-   ##
==========================================
+ Coverage   49.61%   49.64%   +0.03%     
==========================================
  Files         313      313              
  Lines       10811    10803       -8     
  Branches     2015     2011       -4     
==========================================
- Hits         5363     5362       -1     
+ Misses       5442     5435       -7     
  Partials        6        6              

Impacted Files	Coverage Δ
packages/eas-cli/src/build/android/prepareJob.ts	36.37% <ø> (+1.59%)	⬆️
packages/eas-cli/src/build/ios/prepareJob.ts	34.79% <ø> (+4.79%)	⬆️

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