feat(playground): add support to import existing testing yaml and able to edit relationships and attributes

[soranoo]

Is your feature request related to a problem? Please describe.
The playground is a convenient place to build tests, it has a nice intuitive UI.
However, it still lacks some critical features that make it an ideal place for building tests.

Describe the solution you'd like

1. Add support to import existing testing yaml
2. Able to edit relationships and attributes

Describe alternatives you've considered
n/a

Additional context
n/a