Adopt Kubernetes native Sidecar Containers

[pritidesai]

Tekton Pipelines v0.7 introduced the sidecar support in a task with #936 back in June 2019.

The sidecars are implemented in such a way that the users can specify a list of steps/containers running as sidecars. The entrypoint initializes sidecar containers and waits until they are ready to initiate the step containers. Once all the step containers are done, the entrypoint replaces the sidecar container image with nop to terminate the sidecars.

The existing sidecar implementation has been working great with some caveats. Kubernetes 1.29 introduced an in-built support for sidecar containers.

Tekton community had discussion to adopt Kubernetes native approach to sidecars during the API WG on 01/22/24. The community came to an agreement to continue supporting the custom sidecar implementation for backward compatibility purpose and for older version of Kubernetes. And at the same time, adopt Kubernetes native sidecar implementation for the users running compatible version of Kubernetes. We have identified a list of tasks as part of this effort:

• Introduce a check for the Kubernetes version in the Tekton controller. As part of this task, we need to identify what is the best way to implement this check and when it is most reliable.
• Adopt and implement Kubernetes sidecar container only for a compatible Kubernetes version.
• Tekton Pipelines currently requires minimum of 1.25. Work on changing this minimum to 1.29 if possible after Kubernetes native sidecar container support is tested and validated for some time.
• Once the minimum version is upgraded to 1.29, cleanup code to cleanup the code and delete the custom sidecar implementation.

#1131 documents the need for this feature. And, can be closed once this is implemented.

/kind feature

[vdemeester]

cc @abayer