feat: add v1.6.2 opentofu binary to container

[nitrocode]

what

• add opentofu binary to container
• reuse code for both opentofu and hashi
• shellcheck on scripts/download-release.sh
• hadolint on Dockerfile

why

• Add the opentofu binary so it's available to users who customize their workflows
• I kept the COMMAND_DIR for backwards compatibility but I don't think we should store a directory of terraform versions in here because using tf instead of terraform and opentofu instead of tofu is inconsistent. It's also necessary or there will be softlink conflicts. I'd prefer to store the binaries in a separate directory so we can keep the dir names consistent with the binaries.
• The reason tofu is used instead of opentofu is because tofu is their official binary name

tests

• I have tested my changes by running the following commands

✗ shellcheck scripts/download-release.sh
✗

✗ hadolint Dockerfile
✗

✗ docker build -t atlantis-test:latest -f ./Dockerfile .
 => exporting to image                                                                                                1.1s
 => => exporting layers                                                                                               1.1s
 => => writing image sha256:e69a34ffad7ac6589f23881d651808ea25e24a25d7ce4d8dc984624b7aa96383                          0.0s
 => => naming to docker.io/library/atlantis-test:latest 
✗ docker run --rm -it --entrypoint sh atlantis-test:latest -c 'ls -la /usr/local/bin/tofu*'
-rwxr-xr-x 1 root root 79339520 Feb 22 12:14 /usr/local/bin/tofu
-rwxr-xr-x 1 root root 79339520 Feb 22 12:14 /usr/local/bin/tofu1.6.2
✗ docker run --rm -it --entrypoint sh atlantis-test:latest -c 'ls -la /usr/local/bin/terraform*'
-rwxr-xr-x 1 root root 84475904 Jan 31 14:19 /usr/local/bin/terraform
-rwxr-xr-x 1 root root 64626688 Sep 13 14:28 /usr/local/bin/terraform1.4.7
-rwxr-xr-x 1 root root 65200128 Sep  7  2023 /usr/local/bin/terraform1.5.7
-rwxr-xr-x 1 root root 81002496 Dec 13 17:58 /usr/local/bin/terraform1.6.6
-rwxr-xr-x 1 root root 84475904 Jan 31 14:19 /usr/local/bin/terraform1.7.2

references

• Closes Preinstall opentofu in containers #4337
• OpenTofu releases https://github.com/opentofu/opentofu/releases

[nitrocode]

cc @GenPage @jamengual