Prepare new play environment for pipecd

[khanhtc1202]

What would you like to be added:

Prepare https://dev.pipecd.dev/applications?project=play (play project in dev.pipecd.dev) to be used as new play environment for pipecd.
Also stop play.pipecd.dev environment to reduce operation cost.

Why is this needed:

To reduce the operation cost on play.pipecd.dev, currently it's a separated controlplane

[khanhtc1202]

TODO list

• Prepare application showcase in new play project <- @rahulshendre
• Redirect play.pipecd.dev domain to dev.pipecd.dev/project=play <- @khanhtc1202
• Stop play.pipecd.dev controlplane <- @khanhtc1202