Support pod logs with multiple containers

We were unable to reach the second MVC as part of our initial pod log work (https://gitlab.com/gitlab-org/gitlab-ee/issues/4752), which included support for switching between multiple containers in a pod. We should add this support, since this is not uncommon.

Currently, we only expose the first container's logs and error if multiple containers are present

MVC.2

• It has the dropdowns in the header, so users can select the containers.
• The width of dropdown is 360px since the containers sometimes have the long names.
• It has timespan of the logs on the bottom of the logs frame. (Optional, nice to have.)

Design spec

https://gitlab-org.gitlab.io/gitlab-design/hosted/hazel/ee%234752-kubernetes-pod-logs-spec-previews/