Increase minimum core to 10.1 and minimum PHP to 8.1

Problem/Motivation

Given that this module does not yet have a stable release and development will continue for a while before that happens, and that both Drupal core 10.0 and PHP 8.0 will stop receiving security updates in the next couple of months at the time of writing (October 2023), I'd like to increase the minimum requirements for the 2.x branch to Drupal core 10.1 and PHP 8.1. Additionally, the blocking #956186: Allow AJAX to use GET requests was merged into Drupal core 10.1.x, making it tricky to support patching both Drupal core 10.0.x and 10.1.x at the same time.

Steps to reproduce

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Proposed resolution

See problem above.

Remaining tasks

Do the thing.

User interface changes

None?

API changes

None?

Data model changes

None?