`debug` should make suspending on start to be configurable

`debug` currently configures containers to be in a _continue mode_ where the containers run without suspending. It can be useful for users to be able to connect to their containers immediately on execution, such as to debug a `main()` or `init()` method.

_Proposal:_ `debug` should look at the container and/or pod for a _suspend_ option and if present, then configure the pod to suspend on start (where possible). Suggestions are:
- `SKAFFOLD_DEBUG_SUSPEND` environment variable
- pod annotation for a `skaffold.dev/debug/suspend`