Add container registryOverride option

[pditommaso]

This PR adds an container level config that allows override the registry name then when container name specify a fully qualified repository name,

for example:

process.container = "quay.io/my/container:latest: 

and having in the config

docker.registry = "community.wave.seqera.io" 
docker.registryOverride = true

the final resolved container used by the task execution is going to be

community.wave.seqera.io/my/container:latest

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[pditommaso]

It could also be explored if it could make sense to have a more compact notation like:

docker.registry "custom.repo.io", override: true

It should be checked if this is going to work when Wave is enabled.

[bentsherman]

@stevekm would this work for you? See the changes to ContainerHandlerTest to understand how container images would be rewritten

[ewels]

@bentsherman the additional levels of URI hierarchy that I mentioned is with GitLab, see their docs:

registry.example.com/group/project/image:tag

/project/ represents one extra layer compared to normal - I have a feeling it can also have more layers, with sub-projects.

There may be others as well. Not sure if it's relevant to this PR or not (I think not?), but thought I should flag it.