Don't specify registry specific path

[jcansdale]

Why:

The authenticate-packages.md componet is used across all GitHub Package ecosystems. We shouldn't include the ecosystem specific path on the example.

Here are some ecosystem specific URLs that are used:

nuget.pkg.github.com/OWNER
maven.pkg.github.com/OWNER/REPOSITORY
docker.pkg.github.com/OWNER/REPOSITORY/IMAGE-NAME

We could generalize it to simply mention PACKAGE-REGISTRY.pkg.github.com.

What's being changed:

Change Docker specific PACKAGE-REGISTRY.pkg.github.com/OWNER/REPOSITORY/IMAGE-NAME to generic PACKAGE-REGISTRY.pkg.github.com.

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[janiceilene]

Thanks @jcansdale! I'll get this triaged for review ⚡

[lecoursen]

Thanks @jcansdale! I'll merge this now!✨

[github-actions]

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