Prepare custom code for a new Drupal major version

Problem/Motivation

Current code is not Drupal 10 compatible, we should provide necessary changes in the code before the project fully support Drupal 10

Remaining tasks

1. Review and apply fixes from "Automated Drupal 10 compatibility fixes" issue along with other custom fixes.
2. Drop drupal core 8 support
3. Ensure that core_version_requirement is at least ^9 || ^10
3.1. In some cases it could be ^9.3 || ^10 or ^9.4 || ^10 (depends on the core services/changes used in the code), so choose the minimum core version wisely.
4. Follow this article to scan the code and replace deprecation https://www.drupal.org/docs/upgrading-drupal/prepare-major-upgrade/depre...