fix: add flag that allows us to control al2 rollout independent of buildbot

[Skn0tt]

Summary

As explained in https://github.com/netlify/pod-dev-foundations/issues/581#issuecomment-1731022753, enabling the zisi_golang_use_al2 flag will lead to failures in versions of the CLI that don't have the #6020 patch. That means we need to decouple the rollout of zisi_golang_use_al2 in buildbot (where @netlify/build is always up-to-date) from the rollout in the CLI, where the flag also affects versions with broken behaviour. That's why this PR adds a second flag, which we can use to control the CLI rollout independently.

Part of https://github.com/netlify/pod-dev-foundations/issues/581

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[github-actions]

📊 Benchmark results

Comparing with 6aa53d6

• Dependency count: 1,365 (no change)
• Package size: 366 MB (no change)