Ability to provide runtime client

[azuy212]

Is your feature request related to a problem? Please describe. There should be a way to create a runtime client so that we can use credentials fetched from backend.

Describe the solution you'd like Let's say for AWSAppSyncClient if we want to fetch appSync credentials from backend and provide it after app initialization htere should be way to do this.

Describe alternatives you've considered I can't find any alternative for this.