[Discussion] Layotto and Capa non-standard API.

@seeflood For practical use, we have added several sets of `saas api` for [layotto](https://github.com/mosn/layotto) and [capa](https://github.com/capa-cloud/cloud-runtimes-jvm) in the past, E.g:

+ native `s3` api
+ simple `crypto` api
+ `email` api
+ `sms` api
+ `phone` api

an enhanced standard api, E.g:

+ pubsub `delay_queue` api

These apis are used in [layotto api](https://github.com/mosn/layotto/tree/main/spec/proto/extension/v1) and [capa api](https://github.com/capa-cloud/cloud-runtimes-jvm/tree/master/cloud-runtimes-api/src/main/java/group/rxcloud/cloudruntimes/domain/saas), maybe we can share our experience in **api-sig** firstly for discussion and publicity.

In order to better integrate with standard api in the future.

Review the Layotto extension API and Capa SaaS API links, then read the existing discussion in api-sig. The issue proposes sharing experience and discussing future standard API integration, but it names no concrete implementation target or completion criteria.

Written by the indexing model from the issue text.