[async API] Automatic conversion of an API to async

[techsavvyash]

Description

Stencil should automatically turn the APIs async -- event based and then provide results once the processing is finished.

References:

• https://www.asyncapi.com/docs/reference/specification/v2.0.0
• https://github.com/flamewow/nestjs-asyncapi -- this does only documentation we want to do more