Is your feature request related to a problem? Please describe.
We would like to use InitContainers for sidecar containers, given that the lifecycle is better managed, but port assignment in Agones currently only looks for the containers in Containers meaning the sidecars cannot use external ports.

Describe the solution you'd like
https://github.com/googleforgames/agones/blob/main/pkg/apis/agones/v1/gameserver.go#L731

Here, InitContainers with an Always restart policy should be considered.

Describe alternatives you've considered
None, there is no other way to do this.

Additional context

Link to the Agones Feature Proposal (if any)

Discussion Link (if any)