feat: add RCT_IGNORE_PODS_DEPRECATION env variable to pod install

[szymonrybczak]

Summary

Now it's not recommended to run manually pod install, and users should invoke CLI instead, but under the hood in CLI we also execute pod install so to skip the warning we need to pass RCT_IGNORE_PODS_DEPRECATION env variable

Test Plan

1. yarn ios should install Cocoapods without emitting warning.

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).