feat(mix): Support private hex repos/registries

[bryannaegele]

Changes

This adds support to the mix manager to add private hex repos/registries via registryAliases for mapping and hostRules for authentication.

Context

This is the companion to #29756 and dependent on that change. Splitting the manager and datasource work per request in #29756. When combined, this will enable support for private repos/registries such as oban pro.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

Tested in combination with #29756. This will not fully work without that code.