(#1541) Add priority ordering for repository optimizations

[AdmiringWorm]

Description Of Changes

This pull requests re-adds the ability to order sources by priority when installing and upgrading packages.

Motivation and Context

Priority currently are not respected due to to sorting is done on prioritized sources.

Testing

1. Manually set a higher priority on a source containing a package in a non-prioritized source with a lower version available.
2. Call Chocolatey installation command and see what package version would be installed.
3. Do the same test with both sources being unprioritiesed.
4. Do the same test with both sources being the same non-zero priority.

Change Types Made

• Bug fix (non-breaking change)
• Feature / Enhancement (non-breaking change)
• Breaking change (fix or feature that could cause existing functionality to change)

Related Issue

Fixes #1541

Change Checklist

• Requires a change to the documentation
• Documentation has been updated
• Tests to cover my changes, have been added
• All new and existing tests passed.

[gep13]

A couple minor changes based on a quick review.

[gep13]

@AdmiringWorm would it be possible for you to update this PR with the new template that we are using in other repositories, i.e. include information about the testing that was performed (in addition to the new tests which have been added - thanks for getting those added!)

[AdmiringWorm]

@gep13 I have fixed the requested changes, updated the template for the PR and changed the PR to target the develop branch (instead of the old master branch).

The testing steps added was added from memory, and not the same exact steps I had done back when I opened the PR.

[gep13]

LGTM!

[gep13]

@AdmiringWorm I am going to go ahead and get this merged in. The failing AppVeyor build is something that I need to look at, but it is not as a result of the changes in this PR, since the GitHub Action builds are completing successfully.