kong-app release v4.0.0

This is a major release because it changes the default behaviour of the Chart.

For Kong Enterprise deployment the flag .Values.image.repository and .Values.image.tag can now be omitted.
For Kong OSS deployment the flag .Values.image.repository and .Values.image.tag now have to be set to the respective OSS values. For further instructions please refer to the README.md.

Align with upstream chart commit 07ddc3d (ahead of release 2.38.0) (Changes in upstream repository)
Updated handling of session_conf_secret to accommodate Kong 3.6 - Ref
Configure Chart for Kong Gateway Enterprise deployment by default. Please check the README.md to see how to run kong OSS.
Update README.md to reflect default deployment Changes.