Prompts managements

[kerthcet]

What would you like to be added:

For inference scenarios, prompts management is an important part of it.

Why is this needed:

Easy to use for inference users.

Completion requirements:

This enhancement requires the following artifacts:

• [x] Design doc
• [x] API change
• [x] Docs update

The artifacts should be linked in subsequent comments.

[kerthcet]

/kind feature

[kerthcet]

Handle this to the open-webui instead right now. /close