[FEATURE REQUEST] The task details can display the complete payload

[overbeck]

Copied from hibiken/asynq/#636

Is your feature request related to a problem? Please describe.

Currently, the payload of task details cannot be fully displayed. If it exceeds the limit, it will be omitted, and the data that needs to be viewed for task delivery cannot be fully viewed.

Describe the solution you'd like

1. I hope to support viewing the full payload content
2. If it cannot be fully displayed, I hope that a copy button can be added next to the payload display, so that the developer can copy the complete payload and check it by himself

Describe alternatives you've considered

Additional context

[Akshay P J]

@shuqingzai I understand that this is something we all needed. I will create a PR for this.