[Core Feature] [flytekit] Map support for Pod Tasks

[wild-endeavor]

Map support for Pod Tasks

Motivation

Currently the map_task construct only works for regular PythonFunctionTasks. Pod tasks are close enough to regular function tasks however that they should be supported as well.

Goal

To be able to map over Pod Tasks and have the correct PodSpec applied to the run-time pod.

Alternatives

None

Additional Context

Currently the container object generated by the map task looks something like this, when mapping over a basic PythonFunctionTask.

      container {
        image: "flytecookbook:core-732e20036452a7798086bf5abee1ede985f25e51"
        args: "pyflyte-map-execute"
        args: "--inputs"
        args: "{{.input}}"
        args: "--output-prefix"
        args: "{{.outputPrefix}}"
        args: "--raw-output-data-prefix"
        args: "{{.rawOutputDataPrefix}}"
        args: "--resolver"
        args: "flytekit.core.python_auto_container.default_task_resolver"
        args: "--"
        args: "task-module"
        args: "core.control_flow.map_task"
        args: "task-name"
        args: "a_mappable_task"
        resources {
        }
        env {
          key: "FLYTE_INTERNAL_CONFIGURATION_PATH"
          value: "/root/sandbox.config"
        }
        env {
          key: "FLYTE_INTERNAL_IMAGE"
          value: "flytecookbook:core-732e20036452a7798086bf5abee1ede985f25e51"
        }
      }
      task_type_version: 1
    }

This ends up actually kinda working, since Pod tasks are closely related to regular function tasks, but all the Pod dependencies are missing.

The custom field in the map task TaskTemplate today is an ArrayJob. We'll have to figure out how to add the PodSpec in addition to the ArrayJob, and how to invoke the Pod plugin instead of just the container plugin.

This is related to #1050

[jeevb]

@apatel-fn: FYI