Feature/anonymous causer

[Jhnbrn90]

fixes #567

Adressing the comments by @Gummibeer on previous PR #604 regarding issue #567

This PR adds a causedByAnonymous() method, which can be chained from the activity() helper, resolving the causer_id and causer_type to null.

[Gummibeer]

And the last thing: can you add it to the documentation? I would prefer it as a simple hint/sentence, like the default causer in https://docs.spatie.be/laravel-activitylog/v3/basic-usage/logging-activity/#setting-a-causer

[Jhnbrn90]

And the last thing: can you add it to the documentation? I would prefer it as a simple hint/sentence, like the default causer in https://docs.spatie.be/laravel-activitylog/v3/basic-usage/logging-activity/#setting-a-causer

PR #607

[Gummibeer]

https://github.com/spatie/laravel-activitylog/releases/tag/3.9.0