Add support for batch save models in DataStore

[thisisabhash]

Is your feature request related to a problem? Please describe.

[On behalf of a customer] Currently, Datastore supports storing one item at a time:

Amplify.DataStore.save(_ model: M, where condition: QueryPredicate? = nil)

Describe the solution you'd like

An API to save a list or batch of items. Something like:

Amplify.DataStore.save(_ model: [M], where condition: QueryPredicate? = nil)

Describe alternatives you've considered

None

Is the feature request related to any of the existing Amplify categories?

DataStore

Additional context

A similar issue is opened for the API category: https://github.com/aws-amplify/amplify-swift/issues/3434