v2.1.0 SPM support

What’s New:

• Support Swift Package Manager feature
• Updated supported appmetrica_plugin version to 3.2.0.
• Support work with different push providers (Firebase, RuStore, HMS).
• Add method do get payload from notification.
• Updated native SDK versions: Android to 4.1.1, iOS to 3.1.

Full Changelog: v2.0.0...v2.1.0