Add docs on building a CI/CD pipeline for SI

[NatashaWso2]

Description:
It would be good to have docs on building a CI/CD pipeline for SI similar to MI [1]. As of now, when we want to build a CI/CD pipeline for SI we always refer to the blog post written for SP [2]

[1] https://apim.docs.wso2.com/en/latest/install-and-setup/setup/mi-setup/deployment/mi-cicd-overview/
[2] https://medium.com/siddhi-io/building-an-efficient-ci-cd-pipeline-for-siddhi-c33150721b5d

Suggested Labels:
Documentation

Affected Product Version:
SI 1.x