Add Android App Links guidance to https schemes

[ajyong]

• [x] All new/changed/fixed functionality is covered by tests (or N/A)
• [x] 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.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

```diff @@ 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](https://app.codecov.io/gh/auth0/auth0-flutter/pull/324/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | Coverage Δ | | |---|---|---| | [auth0_flutter](https://app.codecov.io/gh/auth0/auth0-flutter/pull/324/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `100.00% <ø> (ø)` | | | [auth0_flutter_android](https://app.codecov.io/gh/auth0/auth0-flutter/pull/324/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `?` | | | [auth0_flutter_ios](https://app.codecov.io/gh/auth0/auth0-flutter/pull/324/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `?` | | | [auth0_flutter_platform_interface](https://app.codecov.io/gh/auth0/auth0-flutter/pull/324/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `87.03% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0#carryforward-flags-in-the-pull-request-comment) to find out more. [see 23 files with indirect coverage changes](https://app.codecov.io/gh/auth0/auth0-flutter/pull/324/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.