Display warning message on invalid redirect in CSV

Problem/Motivation

The path_redirect_import module currently lacks a feature to notify users when no valid redirects are found in the uploaded CSV for deletion. This results in confusion and lack of feedback for end-users.

Steps to reproduce

Upload a CSV file to delete redirects in the module.
Ensure the CSV does not contain valid redirects for deletion.
Observe that there is no warning or error message displayed.

Proposed resolution

Introduce a patch that adds a warning message functionality. This patch triggers a warning message when a user tries to delete redirects but the uploaded CSV file does not contain valid data for the operation.

Remaining tasks

Review and test the patch.
Merge the patch into the main module after community feedback and approval.

User interface changes

The patch will introduce a new warning message on the UI when specific conditions are met (invalid data for deletion in CSV).

API changes

None.

Data model changes

None.