Introduce option -multi-dist to the publish commands

[nresare]

This change makes it possible to publish multiple distributions with packages named the same but with different content by changing structure of the generated pool hierarchy. The option not enabled by default as this changes the structure of the output which could break the expectations of other tools.

Fixes #486

Requirements

All new code should be covered with tests, documentation should be updated. CI should pass.

Description of the Change

Given #486 and and this discussion on aptly-discuss it seems I am not alone in using aptly to self-publish some packages for a handful different distributions and wanting to publish different packages with the same filename for different distributions. As it stands, due to aptly using the default directory structure for the pool hierarchy, aptly will currently fail to publish such packages.

A casual look at the DebianRepository/Format page seems to indicate that the structure of the pool hierarchy is not specified, and as long as the Filename field in Packages references the relevant file any structure could be used.

This change introduces a new option -multi-dist that will create per distribution subdirectories under pool such that each distribution can have its own copy of some package and need not worry about two packages with the same name but different distributions colliding.

One could argue that it would be better to change the default behaviour, rather than implementing a new option, but I feel I have limited visibility into all the implications here, so having this behaviour be enabled on an opt-in basis seems the choice with less risk of functionality regressions. This change can also have storage efficiency implications, so having it be optional seems preferable for that reason as well.

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

[neolynx]

looks great ! thank you so much 👍

would you mind adding a PR to https://github.com/aptly-dev/www.aptly.info and documenting this option ?
then we can merge it !