added phpmyadmin to sail's services

[abedcodes]

Hi everyone,
I use phpmyadmin as database gui client all the time. it is easy & ready to use. this PR adds phpmyadmin to list of services in sail:install & sail add commands. after sail up, phpmyadmin is available at http://localhost:8080. you can change port in docker-compose.yml file if you want.

Best Regards,
MuhammadAli

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If possible, please consider releasing your code as a package so that the community can still take advantage of your contributions!

If you feel absolutely certain that this code corrects a bug in the framework, please "@" mention me in a follow-up comment with further explanation so that GitHub will send me a notification of your response.