Rename `getAccessTree()` to `getHierarchy()` in `ItemsStorageInterface` implementations

[arogachev]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	✔️

[what-the-diff[bot]]

PR Summary

• Removed a line in the Pull Request Template
  • The instruction to include a comma-separated list of tickets addressed by the pull request has been removed. This mean, going forward, you don't need to list out all tickets.
• Log Updated in the ChangeLog
  • We've added information about renaming a method from getAccessTree() to getHierarchy() in ItemsStorageInterface. This update is meant to make it easier to understand what's happening within the system.
• Raised Required PHP Version
  • The minimum required PHP version has been updated from 8.0 to 8.1 in the project's general instructions. This means we now need a slightly more recent version of PHP to ensure the system runs smoothly.
• Renamed Methods in Core Files
  • The method getAccessTree(string $name): array has been renamed to getHierarchy(string $name): array in several files (CteItemTreeTraversal.php, MysqlItemTreeTraversal.php, ItemsStorage.php). This is part of a broader terminology change to make the code more intuitive and readable.
• Changed Test Methods
  • Several methods in the ItemsStorageTest.php file were updated. Tests for removal and retrieval of content from the system will now use the more intuitive getHierarchy method instead of the former getAccessTree method. These updates ensure our tests stay relevant and are fully capable of checking the new system changes.

[codecov[bot]]

Codecov Report

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

Comparison is base (4f97cb1) 99.10% compared to head (053d5a2) 100.00%. Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #68 +/- ## ============================================= + Coverage 99.10% 100.00% +0.89% Complexity 158 158 ============================================= Files 11 11 Lines 673 661 -12 ============================================= - Hits 667 661 -6 + Misses 6 0 -6 ```

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