Change usage of "container" to "container registry"

[jcansdale]

Why:

Users are potentially confused by references to "container support". For example:

Ok, I'll check it out. I didn't do it because GitHub Container Registry is a term which lead me to think is for storing containers instead of images.

https://github.zendesk.com/agent/tickets/980826

What's being changed:

• Change "Container guides for GitHub Packages" to "Guides for GitHub Container Registry"

Check off the following:

• 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]

@jcansdale Thanks for opening a PR! I see this is still in draft mode. Feel free to ping me when you're ready for a writer review and I'll get this triaged ⚡

[janiceilene]

It looks like our new action inadvertently closed this 🙃 Sorry about that! Reopening 💛

[jeremyepling]

We should close this PR or adapt it to use the updated naming scheme - https://docs.google.com/document/d/1BhHuQ7PhPf_ZTOjk2LYi4c-xUBrr9RUowmgkVeU_rXA/edit#

[jcansdale]

@jeremyepling 👋🏻 I like @clarkbw's Container registry guide suggestion here:
https://github.slack.com/archives/CM82WM3LY/p1614117030013700?thread_ts=1614075029.012500&cid=CM82WM3LY

I'm going to close this PR and defer to the updated naming scheme. 😄