agent: support upgrading to newly published k8s versions

In current offline bootstrap design, the k8s assets bundle is associated with the agent version. However, there are use cases where oeprator might want to upgrade to newer k8s versions that not being published associated with the in use agent version. We need a way to simplify the operator workflow here and unblock this usage.

Start by reading the offline bootstrap design and tracing how the Kubernetes assets bundle is associated with the agent version. Define the operator workflow needed to upgrade to a newer Kubernetes version that is not bundled for the current agent, then verify that this workflow works without changing the in-use agent version.

Written by the indexing model from the issue text.