Invalidate a purger's cache from UI

Patch #2 works fine on our side. Thanks!

There is one limitation though: the form shows no success or error message when submitted.

This is because the patch is using drupal_set_message() which is now deprecated https://www.drupal.org/node/2774931 →

Attached is a new patch that replaces drupal_set_message() with \Drupal\Core\Messenger\MessengerInterface::addMessage() as recommended by the change record above.

The last submitted patch, 10: purge-2853613-10.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

Somehow the bot says a test about conditional access is failing. The changeset added in #10 only addresses a messenger deprecation so it is not clear how this is related.

Here is an attempt to resolve this, let's see what the bot says...

Patch does not apply anymore against 8.x-3.x -- re-rolled

purge-2853613-12.patch patch works well and the code looks very solid however unfortunately I had no time to do a detailed review/report but definitely a good candidate to merge.

I have tried the patch purge-2853613-12.patch and it works as expected. I can provide screenshots if this is wanted .