Only build 2 architectures by default

[adhorodyski]

--extra-params -PreactNativeArchitectures=arm64-v8a,x86_64 should be the default.

[thymikee]

Added the architectures input to the action. Can you test this PR? #5

You'll need to point to callstackincubator/android@feat/architectures and replace rnef-build-extra-params with architectures: 'arm64-v8a,x86_64'