Add Android App Links guidance to https schemes

[ajyong]

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

📋 Changes

Surfacing an important step when setting up Android apps to support https schemes.

📎 References

Aligning the Pub.dev docs with the same level of convenience as guidance found in other Auth0 documentation surrounding the use of https schemes:

• https://auth0.com/docs/quickstart/native/flutter/interactive#configure-android
• https://auth0.com/blog/get-started-with-flutter-authentication/#Configure-the-SDK

🎯 Testing

Docs-only change, should not affect tests.

[Widcket]

Thanks @ajyong!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (253209a) 96.08% compared to head (90fdb60) 95.79%.
Report is 8 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #324      +/-   ##
============================================
- Coverage     96.08%   95.79%   -0.30%     
============================================
  Files            97       76      -21     
  Lines          1611     1118     -493     
  Branches        331      281      -50     
============================================
- Hits           1548     1071     -477     
+ Misses           49       46       -3     
+ Partials         14        1      -13     

Flag	Coverage Δ
auth0_flutter	100.00% <ø> (ø)
auth0_flutter_android	?
auth0_flutter_ios	?
auth0_flutter_platform_interface	87.03% <ø> (ø)

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see 23 files with indirect coverage changes

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