chore: add ios/Gemfile for emb CI build

emb internally runs `cd ios && bundle install`, requires Gemfile
with fastlane and cocoapods dependencies.
3 jobs for main in 1 minute and 19 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #127588
studio triggered
ci-build

00:01:19

failed #127479
studio triggered
ci-build

00:01:12

failed #127478
studio triggered
ci-build

00:01:22

 
Name Stage Failure
failed
ci-build Build
  output: [ null, null, null ],
pid: 26378,
stdout: null,
stderr: null
}

Node.js v18.20.4
Cleaning up project directory and file based variables
ERROR: Job failed: exit status 1