Remove k8s start command for now

[katiewasnothere]

Type of Change

• Breaking change

Motivation and Context

The container k8s start command was added to the k8s subcommand to support starting a previously stopped cluster node. Since cluster nodes show up in the higher level container commands such as container ls and container stop, it made sense to have the ability to additionally start control plane nodes for the k8s clusters with container k8s start. However, since adding this subcommand, we've seen a number of issues around restarting (see 1) and we additionally have concerns about what the UX design should be for the k8s plugin moving forward.

Since this is an experimental feature, this PR will remove k8s start for now while we work on improving the plugin overall. This will not only make the code easier to reason about from a developer point of view but additionally gives users less ways to potentially shoot themselves in the foot while we improve the feature.

If a control plane node is stopped in a cluster, in lieu of k8s start, to restart it, a user will need to delete the cluster with container k8s delete and re-create it with container k8s create.

We're open to feedback on this decision and use cases for k8s start.

Testing

• Added/updated docs

[github-actions]

Code Coverage

Tier	Line Coverage
Unit	24.93%
Integration	66.77%
Combined	76.21%