Storage Image should have a configurable image provider

[lesnitsky]

StorageImage should have a configurable image provider, to allow local caching, similar to https://pub.dev/packages/firebase_cached_image.

It would make sense to configure a top-level image provider, so FirebaseUIStorageConfiguration will need an additional property defined and taken into account.

cc @russellwheatley

[github-actions]

Hello 👋, to help manage issues we automatically close stale issues.

This issue has been automatically marked as stale because it has not had activity for quite some time. Has this issue been fixed, or does it still require attention?

This issue will be closed in 15 days if no further activity occurs.

Thank you for your contributions.

[github-actions]

Hello 👋, to help manage issues we automatically close stale issues.

This issue has been automatically marked as stale because it has not had activity for quite some time. Has this issue been fixed, or does it still require attention?

This issue will be closed in 15 days if no further activity occurs.

Thank you for your contributions.