Make container image rule compatible with Bazel 8

[justinwon777]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

I am able to build container_image with Bazel 8 on this change.

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Bazel 8 removes the api to_json() which is used in this file.

What is the new behavior?

Replace it with json.encode()

Does this PR introduce a breaking change?

• Yes
• No

Other information

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[linzhp]

The CI is set up to use Bazel 4. We need to change it to Bazel 8 in order to test this PR