New extraInitContainers configuration added.
It allows to pass template with a list of containers to execute before
main code-server container started. Main container will only start when
all init containers are completed (exited with 0 code).
Additionally changes the way extraContainers is used - instead of
toYaml use tpl, because this allows to
reference any values from extraContainers string.
Microsoft publishes updates to this action using the same scheme
as GitHub, where the v1 tag is updated to the latest release of
the 1.0 series. Therefore, we can manage updates manually.
