Respect poetry explicit source

[lucemia]

Context

• The issue dependabot updater still check poetry explicit source  #7918 is being addressed to incorporate support for Poetry's explicit package source.
• Following this update, the explicit package source will only be utilized if a package explicitly specifies it as the source.

Poetry 1.5.0 introduced the concept of an explicit package source, which can be found here: Explicit Package Sources.

If package sources are configured as explicit, these sources are only searched when a package configuration explicitly indicates that it should be found on this package source.

Summary of Modifications

• An update has been made to the pyproject_files_parser, which previously ignored package source configuration in pyproject.toml but will now correctly read the value.
• The index_finder has also been updated to ignore any source marked as explicit unless it is specified as the source of the package.

Testing

• test with ./bin/dry-run.rb and check explicit package source won't be consider unless it is defined as the source of a package

User facing changes

• a source marked as explicitly, won't be check for package that not specified it as source
• other behavior should be the same

To-Do:

• based on the document package-source-constraint, If a package specifies a source, it should not check other sources. Currently all sources (except explicitly) will still be considered

A repository that is configured to be the only source for retrieving a certain package can itself have any priority. In particular, it does not need to have priority "explicit". If a repository is configured to be the source of a package, it will be the only source that is considered for that package and the repository priority will have no effect on the resolution.

Fixes #7918.

[deivid-rodriguez]

This looks great.

I added a few nitpick comments, nothing that blocks merging this as is, really, but feel free to address!

[deivid-rodriguez]

Looks great now, could you squash all commits into one to simplify git history?

[lucemia]

@deivid-rodriguez done!

[deivid-rodriguez]

Awesome, I will merge and deploy this later today! Thanks for the great work 💪

[deivid-rodriguez]

Thanks so much for the nice contribution!