[Consider] Keep track of a source which contains a package

[mishra14]

We should allow users to correlate a package with a source. This will prevent the initial discovery phase and the corresponding http calls to all the sources till the package is pulled down into the cache.

Possible solutions (In the order of preference)-

1. Allow users to correlate a source with packages in NuGet.Config files.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
  </packageSources>

  <packageDependencies>
    <nuget.org>
      <package id="PackageThatIsOnlyOnNuGet.Org"/>
    </nuget.org>
  </packageDependencies>
  
</configuration>

2. Create a new restore graph file.
3. Write the information into the NuGet.Cache file that will be added with restore no-op work.
4. Write down this info into the assets file and make restore use that.

[nkolev92]

Related to #6867

[MV10]

Ideally we could also indicate that it should only come from the source. Particularly during active development with a local source, caching just gets in the way. This is badly needed.

[nkolev92]

Fixed by NuGet/NuGet.Client#3785.

Ideally we could also indicate that it should only come from the source. Particularly during active development with a local source, caching just gets in the way. This is badly needed.

Yep, definitely something on our radar. #6867 and #6579 are the 2 related issues.