Move end-to-end tests to dedicated test directory

[jaegeral]

WARNING: This PR will likely have broken end2end tests for Github.

This pull request moves the end-to-end tests from ./end_to_end_tests to ./tests/end_to_end_tests. This change streamlines the project's folder structure by consolidating all test-related files within the tests directory. This improves organization and makes it clearer where different types of tests reside.

Specifically:

• Moved the ./end_to_end_tests directory and its contents to ./tests/end_to_end_tests.
• Updated any references to the old end-to-end test path within the codebase to reflect the new location. (If applicable, list specific files or modules that were updated. E.g., "Updated references in run_e2e_tests.sh and configuration files.")

This change aims to improve the overall project structure and maintainability. It does not introduce any new functionality or change existing behavior. Keeping all tests within the tests directory allows for better organization and discoverability of both unit and end-to-end tests.

Checks

• All tests succeed.
• Unit tests added.
• e2e tests added.
• Documentation updated.

Closing issues

Related to #3184

[jaegeral]

This might be a bit more involved then expected. I will keep the PR as draft for now.

In case it is open for one year, it shall be closed.