fix: calculate resolvedOfferings for sidecars

[g-linville]

@tylerslaton reported this issue to me this morning. My previous implementation of this was taking the resolved offerings for a container and setting them for all sidecars on the container as well. Not sure what I was thinking, because that was very incorrect. With this PR, sidecars get their offerings resolved the same way that normal containers do.

Checklist

• [x] The title of this PR would make a good line in Acorn's Release Note's Changelog
• [ ] The title of this PR ends with a link to the main issue being address in parentheses, like: This is a title (#1216). Here's an example
• [x] All relevant issues are referenced in the PR description. NOTE: don't use GitHub keywords that auto-close issues
• [x] Commits follow contributing guidance
• [x] Automated tests added to cover the changes. If tests couldn't be added, an explanation is provided in the Verification and Testing section
• [x] Changes to user-facing functionality, API, CLI, and upgrade impacts are clearly called out in PR description
• [ ] PR has at least two approvals before merging (or a reasonable exception, like it's just a docs change)