[8.x] TaggedCache flush should also remove tags from cache

[Plytas]

At the moment flushing a tagged cache removes standard keys, forever keys and the key/value pair that was actually cached, but it leaves the tag itself as it only resets it.

In our project we use renoki-co/laravel-eloquent-query-cache and with heavy cache tag usage it leads to junk keys accumulating in our redis instance to a point where we now have close to 5 million keys that will never expire:

IMO, cache tags (as well as standard keys) should have an expiration time as well, but I'm able to solve that in userland by setting expiration time to them manually after caching the value. But it doesn't solve the issue when you flush a tag.

This PR solves flushing issue by deleting the tags from cache instead of resetting them. I've added a small test that you can run without TaggedCache changes and see that the tag key actually persists after flush.

[taylorotwell]

Are you using Redis? If so, can you just implement this change on the RedisTaggedCache (you can still add a method to TagSet)? That way we are making a smaller change.

[Plytas]

I've reverted TaggedCache and implemented the change on RedisTaggedCache. I had to remove my newly added test because it was using ArrayStore, thus not being impacted by this change. Not sure if possible to write a test without mocking that would prove that tags are being removed.

Link to previous test for reference