feat: (IAC-1065) Add Hadolint, ShellCheck and TFLint Checks via GitHub Actions

[jarpat]

Changes

Enabled linting of the viya4-iac-gcp project with Hadolint, ShellCheck and TFLint through a workflow in GitHub actions. Once the workflow was configured, any errors or warnings raised was resolved as part of this PR.

No change in functionality has been made with this PR mostly formatting, notably some changes that were made as per recommendation of TFLint:

• terraform_unused_declarations
  • removed unused variables in locals.tf and variables.tf files
• terraform_deprecated_index
  • We were using a legacy form of referring to indexes in our list variables
  • We were using the legacy form of splat expressions https://developer.hashicorp.com/terraform/language/expressions/splat#legacy-attribute-only-splat-expressions
• terraform_typed_variables
  • some variables in our variables.tf were not typed

Additionally missing doc was added to our top and module level variables.tf files and the code was run through a formatter.

Tests

Scenario	Provider	K8s Version	Order	Cadence	Orchestration	Notes
1	GCP	1.26 (v1.26.5-gke.1200)	******	fast:2020	DO	external pg

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