Drop deprecated NetworkProfile option for ContainerGroups

[jemrobinson]

✅ Checklist

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⤴️ Summary

• Update to new ACMEClient syntax
• Add missing priorities to ApplicationGateway routing rules
• Replace ContainerGroup NetworkProfiles with subnet IDs.

🌂 Related issues

Closes #1717

🔬 Tests

Tested on new SRE deployment

[JimMadge]

Can we make sure to get reviews for PRs before merging, even for small changes 🙏

[jemrobinson]

Can we make sure to get reviews for PRs before merging, even for small changes 🙏

Sorry - my fault for trying to open too many PRs that all depended on one another! I'll try to restrain myself in future :)