Rule proposal: enforce depth for modules from Git

[chernetskyi]

Terraform allows to shallow clone the repositories with the modules:
https://developer.hashicorp.com/terraform/language/modules/sources#shallow-clone

Somehow, this feature is not well-known (no one I asked knew about it), but is very beneficial. My team only uses modules with GitHub sources and this small change notably decreased the durations of terraform init. I believe a rule enforcing depth=1 will benefit not only my team. Documentation's wording looks like a recommendation:

For larger repositories you may prefer to make only a shallow clone in order to reduce the time taken to retrieve the remote repository.

I can implement the rule if maintainers agree there is a place for it in this repository.

Regarding the details, I think the rule should be enabled by default and trigger for Git (GitHub, BitBucket) module sources that do not specify raw commit IDs in the ref argument.

[bendrucker]

Interesting, I was also unaware as I've moved on from sourcing modules from git directly. We generally look for recommendations from the Terraform docs for rules in this ruleset, and this meets that criteria. So 👍🏻 to a rule PR.

I'd say it should not be enabled by default given that Terraform positions it as a feature "you may prefer to" enable.