Read docker.registry configuration when checking containers exist

[adamrtalbot]

Description of feature

Currently, the nf-core modules lint can confirm a docker container exists at the remote registry when linting a module. However, if the container name is simple it expects it to be hosted on quay.io. Instead, we should respect docker.registry which may be set to something else. As a simple option, this could be added as a command line parameter e.g. --registry public.ecr.aws until we can automatically read it from the configuration.

[mashehu]

Fixed in #2318