drivers/docker: rename logging type to driver

[notnoop]

Docker uses the term logging driver in its public documentations: in
docker daemon config[1], docker run arguments [2] and in docker compose file[3].
Interestingly, docker used type in its API [4] instead of everywhere
else.

It's unfortunate that Nomad used type modeling after the Docker API
rather than the user facing documents. Nomad using type feels very
non-user friendly as it's disconnected from how Docker markets the flag
and shows internal representation instead.

Here, we rectify the situation by introducing driver field and
prefering it over type in logging.

Doing it here in a backward compatible manner, and will update docs with driver field once 0.9 final ships.

[1] https://docs.docker.com/config/containers/logging/configure/
[2] https://docs.docker.com/engine/reference/run/#logging-drivers---log-driver
[3] https://docs.docker.com/compose/compose-file/#logging
[4] https://docs.docker.com/engine/api/v1.39/#operation/ContainerCreate

[github-actions]

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