Fix installing react-native as a dependency

To support sending files to AWS S3 we recently added a [Send File To S3 service](#293). As part of that change we added `@aws-sdk/client-s3` as a dependency.

Unfortunately, we got hit with 2 things at once. `client-s3` has a dependency on a middleware package that has a **peer** dependency on `react-native`.

Also, npm v7 is out and that automatically installs peer dependencies, even when not really needed.

Until aws/aws-sdk-js-v3#2108 is merged it looks like the workaround is to use the command [`npm install --only=production --legacy-peer-deps`](aws/aws-sdk-js-v3#2150 (comment)). This tells npm to use pre-v7 behaviours and not automatically install peer dependencies.

Author: Cruikshanks