Update NGINX Gateway Fabric communications

[sjberman]

What type of PR is this?

/kind documentation
What this PR does / why we need it:
The NGINX community slack is being sunsetted in favor of the new forum.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @sjberman. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[mikemorris]

/ok-to-test

[mikemorris]

/lgtm

[robscott]

Thanks @sjberman!

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: robscott, sjberman

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