use `testcontainers` instead of interacting with docker directly

[rursprung]

currently you suggest to launch docker manually to run e.g. databases used in tests.
it'd be much more convenient to use testcontainers for this instead.

(full disclosure: i've not yet used testcontainers in rust - never had the need - but use it extensively in java and it's the de-facto standard there and i wouldn't want to go back to manually trying to muck around with docker)