containers: add documentation for using external image registries

[nikitassharma]

Summary

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.

[github-actions]

This PR requires additional review attention because it affects the following areas:

Partials

This PR updates partial files, which are pieces of content used across multiple files in our Render component.

• workers/wrangler-commands/containers - view affected files

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/containers/	@mikenomitch, @th0m, @cloudflare/pcx-technical-writing, @cloudflare/cloudchamber
/src/content/partials/workers/	@cloudflare/workers-docs, @GregBrimble, @irvinebroque, @mikenomitch, @WalshyDev, @cloudflare/deploy-config, @cloudflare/pcx-technical-writing, @kodster28, @cloudflare/wrangler, @cloudflare/workers-runtime-1

[github-actions]

Preview URL: https://3d1d2dc8.preview.developers.cloudflare.com
Preview Branch URL: https://nsharma-external-registries.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/containers/platform-details/image-management/	https://nsharma-external-registries.preview.developers.cloudflare.com/containers/platform-details/image-management/

[mikenomitch]

The docs say "with the following" policy, but this is referencing specific images.

I think we need to rephrase above to show that this is an example.

And/or remove the specific images from this and leave a commented out section referring to a specific image (but keep the splat)?

[nikitassharma]

Updated to be more explicit in the documentation. Also changed the policy to default to the splat and left the specific image as a commented out example

[mikenomitch]

+1ing to unblock you, but some comments that we should address