Allow for dependencies to not be compiled

[sophiewigmore]

Summary

As a part of paketo-buildpacks/dotnet-core#722, the SDK dependency should not be compiled anymore. Instead, it's URI and SHA256 should be the same as the upstream ones.

This PR does two things:

• provides a mechanism to allow dependencies to not be compiled
• marks the .NET SDK dependency as non-compiled.

I have tested the templating behaviour locally.

Use Cases

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).

[fg-j]

Nice! This is a lot simpler than I imagined it would be. 🙂

[sophiewigmore]

@fg-j inspired just a wee bit from #179

[sophiewigmore]

bump @brayanhenao :)