Fix: Saving files in custom data dir not working on Android

[ComputerElite]

This pull request fixes not being able to save or see certain notes when saving in a custom data directory by requesting the MANAGE_EXTERNAL_STORAGE permission when you select a custom data directory.

This way notes can be synced via Syncthing and more.

Closes #1223
Replaces #1442

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 26 lines in your changes missing coverage. Please review.

Project coverage is 47.03%. Comparing base (7d60459) to head (917f42f).

Files with missing lines	Patch %	Lines
...mponents/settings/settings_directory_selector.dart	0.00%	26 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1448      +/-   ##
==========================================
- Coverage   47.15%   47.03%   -0.13%     
==========================================
  Files         114      114              
  Lines        9002     9026      +24     
==========================================
  Hits         4245     4245              
- Misses       4757     4781      +24     

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