Promote AutopilotPassthroughPort feature gate to Alpha

[vicentefb]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug
/kind cleanup
/kind documentation
/kind feature
/kind hotfix
/kind release

What this PR does / Why we need it:
Promote AutopilotPassthroughPort feature gate to Alpha

Which issue(s) this PR fixes:
Work towards #3721

Special notes for your reviewer:

[agones-bot]

Build Failed 😱

Build Id: cde3954b-d307-4d30-a903-69f8ba27065d

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[agones-bot]

Build Failed 😱

Build Id: 7887b0fa-db47-4b05-95d8-dd43a761a611

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[agones-bot]

Build Succeeded 👏

Build Id: c7d9d0b7-5b25-47ce-bd8c-5ad9e8636bd5

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.41.0-dev-b2ecc42-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.41.0-dev-b2ecc42-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.41.0-dev-b2ecc42-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.41.0-dev-b2ecc42-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.41.0-dev-b2ecc42-amd64
• Linux C++ SDK (build): agonessdk-1.41.0-dev-b2ecc42-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.41.0-dev-b2ecc42-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://b2ecc42-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3849/head:pr_3849 && git checkout pr_3849
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.41.0-dev-b2ecc42-amd64

[agones-bot]

Build Failed 😱

Build Id: 291ea974-ddf8-490a-8365-4851a0e3b86b

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[agones-bot]

Build Succeeded 👏

Build Id: d72bce85-2324-4ea6-ba8d-2452563a7ed9

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.41.0-dev-ded8010-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.41.0-dev-ded8010-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.41.0-dev-ded8010-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.41.0-dev-ded8010-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.41.0-dev-ded8010-amd64
• Linux C++ SDK (build): agonessdk-1.41.0-dev-ded8010-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.41.0-dev-ded8010-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://ded8010-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3849/head:pr_3849 && git checkout pr_3849
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.41.0-dev-ded8010-amd64