ci: add tflint to CI workflow

[JoshuaLicense]

Description

Add tflint to CI. Fixes the various warnings reported.

Before submitting (or marking as "ready for review")

• Does the pull request title follow the conventional commit specification?
• Have you performed a self-review of the code
• Have you have added tests that prove the fix or feature is effective and working
• Did you make sure to update any documentation relating to this change?

[github-actions]

Terraform plan for environment: int

Commit: ae4c966

API version: be6a3c6
Selfserve version: be6a3c6
Internal version: be6a3c6

Plan summary

0 to add, 0 to change, 0 to destroy

---

Show full plan

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration
and found no differences, so no changes are needed.

[github-actions]

Terraform plan for environment: dev

Commit: ae4c966

API version: be6a3c6
Selfserve version: be6a3c6
Internal version: be6a3c6

Plan summary

0 to add, 0 to change, 0 to destroy

---

Show full plan

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration
and found no differences, so no changes are needed.

[github-actions]

Terraform plan for account: nonprod

Commit: ae4c966

Plan summary

0 to add, 0 to change, 0 to destroy

---

Show full plan

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration
and found no differences, so no changes are needed.