Add Conditionable to ActivityLogger

[usernotnull]

This PR adds Conditionable trait.

activity()
    ->by($comment->commented)
    ->on($comment->commentable)
    ->when(
        $condition,
        fn (ActivityLogger $logger) => $logger->chainSomething()
    )
    ->when(
        $anotherCondition,
        fn (ActivityLogger $logger) => $logger->chainSomethingElse()
    )
    ->log('comment.created');

The above would be a tidy implementation of something that could get more ugly as more conditions are added.

[Gummibeer]

I like it very much @freekmurze could you release it. Will stop GitHub for today now.

https://gummibeer.dev/blog/2022/end-of-an-era/

[AlexVanderbist]

hey @usernotnull, thanks for your patience and thanks for the great PR. Small change but very useful indeed :D