Our current Terraform setup attempts to create three static files on our
GCS buckets. The issue is that these buckets are configured to
automatically delete files that are older than X days, and there is no
way to exclude specific files from that. Therefore, the created files
disappear after some time, and running `terraform plan` suddenly looks
like the infrastructure has changed.
Moreover, the added value of these three files seems questionable: two
of them provide `index.html` type of functionality for our two caches,
whereas the third is automatically created by `nix` when pushing to the
cache anyway (if it doesn't exist already).
This PR also reduces the cache eviction time for the nix cache to 60
days, as a full year seemed a bit long.
CHANGELOG_BEGIN
CHANGELOG_END
* infra: gcp_cdn_bucket: update comment
The cache retention can be configured, while the comment suggests its
hardcoded.
* infra: don't create index.html inside gcp_cdn_bucket module
We might want to add a different index.html per bucket, so move that
code outside the module and into the bucket-specific terraform files.
Also add bucket-specific index.html files.
