fix(apple): read Gemfile & fallback to globally installed pod

[szymonrybczak]

Summary

Some projects have Gemfile in the root directory but for other purposes, so checking if it's presented is not enough.

This Pull Request adds reading and simple regex to check if gem cocoapods is included which should make the workflow more solid.

Also this Pull Requests adds a fallback if for any reason CLI decided to install with bundle exec pod install we fail silently and fallback to globally installed pod.

Test Plan

1. yarn add react-native-svg
2. Remove Gemfile and run run-ios
3. Cocoapods should be properly installed.

Checklist

• Documentation is up to date.
• Follows commit message convention described in CONTRIBUTING.md.
• For functional changes, my test plan has linked these CLI changes into a local react-native checkout (instructions).

[szymonrybczak]

cc @tido64 I hope that with this one we'll finally make everything work in your setup 🤞