Update rules_bazel page and add to private apk repo page

[matthewhelmke]

This fixes https://github.com/chainguard-dev/internal/issues/5730 and https://github.com/chainguard-dev/internal/issues/5731, the latter of which became an issue because it was super-outdated and the new small section being added to the Private APK Repos page links to it. I couldn't in good conscience link a new section to an outdated page.

This PR:

• Adds a section called Using Private APK Repositories with Bazel rules for apko to the Chainguard's Private APK Repositories page that uses a parallel construction to the existing section it follows and links to the Bazel page for more detail.
• Rewrites most of the Bazel Rules for apko page as the existing page uses Bazel 6 and a number of deprecated features. It now uses Bazel 9, which was released earlier this week. I tested everything on the page extensively using the Chainguard Container for Bazel 9 on my local system. Please read for sanity, but the build and details are correct (and mostly discovered while figuring all this out).

DocsTeam reviewers: Please check me on my headings. I used gerunds for headings that cover multiple sections of procedural steps and imperatives for individual steps. Is this what we use? I can't remember, but it seemed reasonable while I was in the writing flow. Now that we're reviewing, please help me get it right.

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[xnox]

Very good!

[SharpRake]

LGTM! Two comments, the first is non-blocking but the output label should be applied to the last block

[matthewhelmke]

LGTM! Two comments, the first is non-blocking but the output label should be applied to the last block

Thank you! I got them both in that last commit. Merging.