Add support for Knative workloads

[shub970]

Summary

Knative (https://knative.dev/docs/) is picking up fast for efficient management of serverless workloads on the Kubernetes cluster.
It uses its own set of CRDs for different deployment resources. These CRDs, along with other core components can be installed on the cluster easily with kubectl (refer installation docs).
However, ability to manage knative CI/CD workflows using Devtron, is missing.
devtron/generic-helm-charts can be a way to go forward for custom deployments, but can't be integrated into the CI/CD workflow.

Motivation

knative offers a lot of features in terms of handling the eventing of a service. It defines its own Service resource that has a revision lifecycle, just as a regular kubernetes service.
Even if these knative services are deployed through a chart on the cluster, it gets challenging to handle their deployment because of manual intervention (updating and redeploying the charts). These services could be added to an environment like any other kubernetes service and managed through an automated CI/CD pipelines.

Proposal

A way to define knative service in the deployment template and a workflow for it with CI and CD pipelines.