Add iOS support

[evdokimovs]

Synopsis

This PR adds basic support for the iOS platform.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains Draft: prefix
  • [x] Name contains issue reference
  • [x] Has k:: labels applied
  • [x] Has assignee
• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
  • [x] Milestone is set
  • [x] PR's name and description are correct and up-to-date
  • [x] Draft: prefix is removed
  • [x] All temporary labels are removed

[evdokimovs]

FCM

Bootstrap iOS plaform support (#87)

Additionally:
- update Gradle versions for Android platform

[alexlapa]

@tyranron ,

Why flutter/ios/lib/aarch64-apple-ios/libmedea_jason.a is present?

Косяк. Надо еще пустой .pubignore докинуть flutter/ios/.pubignore