Investigate runtime version via env

[kendallroth]

Description

As noted in #9, environment variables can be used to customize Expo app behaviour (from builds or development). This could potentially be utilized to set the Expo config runtimeVersion="sdkVersion" in development (to support Expo Go client) while also supporting runtimeVersion="appVersion" (or native) during builds/updates. The benefit in this would be use of Expo Go in development, while hopefully preventing issues when modifying native code/packages. However, it is highly possible that Expo Go cannot even be utilized with modified native code/packages, which would render this entirely moot, as then using the sdkVersion to limit updates would be completely acceptable.

• EAS Build
• EAS Update