Allow to specify connection in ClearCommand

[antennaio]

This pull request updates the horizon:clear command to allow specifying the connection as an argument. The arguments and options will now match those of Laravel's queue:clear command, making both commands consistent and easy to remember.

Example usage:

• php artisan queue:clear redis --queue=emails
• php artisan horizon:clear redis --queue=emails

Why is it useful?

It will be useful to people who make use of multiple connections. Adding this feature makes it easier to target a specific connection when running horizon:clear. Other Horizon commands already support specifying the connection.