Remove and gitignore `pubspec.lock` files

[Widcket]

• [ ] 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

The auth0_flutter package includes /pubspec.lock in its .gitignore. However, the .gitignore of the auth0_flutter_platform_interface package does not. Yet both pubspec.lock files are present in the repository.

This causes the following warning when publishing auth0_flutter:

Given that:

• Pub docs do not recommend committing lock files (for libraries)
• We added them for CI convenience reasons that no longer apply after the move to GitHub actions

This PR removes both pubspec.lock files, and adds /pubspec.lock to the .gitignore of auth0_flutter_platform_interface package. And also adds **/doc/api to it.

[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 (f2030d9) 90.31%. Report is 23 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #340 +/- ## ============================================ - Coverage 96.08% 90.31% -5.78% ============================================ Files 97 49 -48 Lines 1611 475 -1136 Branches 331 0 -331 ============================================ - Hits 1548 429 -1119 + Misses 49 46 -3 + Partials 14 0 -14 ``` | [Flag](https://app.codecov.io/gh/auth0/auth0-flutter/pull/340/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/340/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `100.00% <100.00%> (ø)` | | | [auth0_flutter_android](https://app.codecov.io/gh/auth0/auth0-flutter/pull/340/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/340/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/340/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | `87.03% <100.00%> (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. | [Files](https://app.codecov.io/gh/auth0/auth0-flutter/pull/340?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0) | Coverage Δ | | |---|---|---| | [...lib/src/web/extensions/user\_profile\_extension.dart](https://app.codecov.io/gh/auth0/auth0-flutter/pull/340?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0#diff-YXV0aDBfZmx1dHRlci9saWIvc3JjL3dlYi9leHRlbnNpb25zL3VzZXJfcHJvZmlsZV9leHRlbnNpb24uZGFydA==) | `100.00% <100.00%> (ø)` | | | [...lutter\_platform\_interface/lib/src/credentials.dart](https://app.codecov.io/gh/auth0/auth0-flutter/pull/340?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0#diff-YXV0aDBfZmx1dHRlcl9wbGF0Zm9ybV9pbnRlcmZhY2UvbGliL3NyYy9jcmVkZW50aWFscy5kYXJ0) | `100.00% <100.00%> (ø)` | | ... and [50 files with indirect coverage changes](https://app.codecov.io/gh/auth0/auth0-flutter/pull/340/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=auth0)

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