[llvm] [CI] Upstream premerge terraform configuration (PR #117397)

[Vlad Serebrennikov via llvm-commits]

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+# Premerge Infrastructure
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+This folder contains the terraform configuration files that define the GCP
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Endilll wrote:

I've found it very useful to be able to make changes to pre-merge configuration and script, and test them right away as a regular PR to the monorepo. It seems that the workflow for zorg changes is less straightforward. Since this PR is concerned with pre-merge stuff, I prefer to keep the changes in the monorepo.

https://github.com/llvm/llvm-project/pull/117397