[Improvement]: Dev docs missing instructions on how to `getDeviceId`

[tina-tan]

What can we improve?

Our Browser SDK has instructions on how to getDeviceId here, but this information is missing for our iOS (beta and legacy) and Android SDKs.

Please review all of our client-side SDK docs to ensure that this is documented. We have clients writing in and asking how they can set this.

Discourse with additional info:

• iOS SDK: https://discourse.amplitude.com/t/ios-sdk-is-the-getdeviceid-call-deprecated/5754
• Android SDK: https://discourse.amplitude.com/t/how-where-do-we-store-device-ids/5572

Which page needs an update?

Both versions of the iOS SDK:

• https://www.docs.developers.amplitude.com/data/sdks/ios/
• https://www.docs.developers.amplitude.com/data/sdks/ios-swift/

Android SDK:

• https://www.docs.developers.amplitude.com/data/sdks/android-kotlin/

React Native:

• https://www.docs.developers.amplitude.com/data/sdks/typescript-react-native/