Consider using hc-install instead of go-getter to install terraform binary

[lukemassa]

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• I'd be willing to implement this feature (contributing guide)

Describe the user story

Terraform recently released version 1.8.2, which changes the way terraform packages its binary led to it being incompatible with atlantis's --tf-download functionality. We worked around this by explicitly ignoring version 1.8.2 (#4474). More information here: #35075.

The recommendation from the TF Core maintainer was to use a hashicorp tool called hc-install: hashicorp/terraform#35075 (comment). This seems in general more robust than what Atlantis is currently doing, and is worth investigating.

Describe the solution you'd like

Investigate the possibility of using hc-install to download and install terraform.

Describe the drawbacks of your solution

I haven't thought about this too much yet, just wanted to open this up for discussion.

Describe alternatives you've considered

We could continue to manually download and install, including extracting the binary more explicitly (#4478).

[james0209]

Hey! Yeah I've opened up a WIP PR to default URL downloads to hc-install - #4494
(custom URL downloads are a little different, explained in PR description)

If anyone has any opions/views/concerns or want to discuss it more please let me know! I replied to a comment in the PR already and started filling in the PR description to make the current logic vs proposed changes easier to understand.