Augment info about Keptn-without-k8s

[StackScribe]

Summary

The Keptn - Kubernetes page discusses running a KeptnTaskDefinition with a deployment that does not run on k8s. It does not cover:

• Explicit information about how to "trigger" the KeptnTask
• How to use the Analysis feature for a deployment that does not run on k8s

Also, the Migration Guide does not mention this capability, although it is of interest to people who have been running Kepnt v1 for deployments on non-k8s platforms

@bacherfl provided this information in https://cloud-native.slack.com/archives/C017GAX90GM/p1704443843493729 so it should be added to the docs

DoD

[x] Keptn-Kubernetes explains how to "trigger" a KeptnTask for a non-k8s deployment
[x] Keptn-Kubernetes discusses the use of the Analysis feature for non-k8s deployments
[x] Migration Guide contains a brief description of what Keptn can do for non-k8s deployments and links to these other docs for details

[StackScribe]

This is fulfilled by #2778