Add support for topologySpreadConstraints

[MikeBlomm]

Is your enhancement request related to a problem? Please describe.
Currently I'm not able to set a topologySpreadConstraints on the nginx pods. This leads to the fact that I can't have finegrained control of the spread over my availability zones.

What would you like to be added:
Support for a topologySpreadConstraints field on the nginx-gateway-fabric Deployment

Why this is needed:
Allow the spread of mutliple availability zones.

[nginx-bot]

Hi @MikeBlomm! Welcome to the project! 🎉

Thanks for opening this issue!
Be sure to check out our Contributing Guidelines and the Issue Lifecycle while you wait for someone on the team to take a look at this.

[mpstefan]

Hey @MikeBlomm, thanks for the feedback! Would you be up to creating a PR for this change? As our backlog is now, we'd need to look at next release, meaning it wouldn't be out in an official release until early next year. If we can get this change in before early Nov, we can squeeze it in for 1.5.

Otherwise, the use case makes sense, and we'll throw it in our backlog!