frontend: Invalid option key when create task

[Prnyself]

When create task with QingStor, the key of option bucket_name is name, not bucket_name.

[Xuanwo]

We need to provide a table of available pairs.

As GSP-90 has been approved, we can build connection string at the front side and service side don't need to handle pairs anymore.

[Xuanwo]

Could be solved via #107