add superlinter and fix linting errors

[glennmusa]

Description

This change introduces GitHub super-linter as a Pull Request linting check, and fixes the existing errors in the repo, for these languages:

VALIDATE_ALL_CODEBASE: true
VALIDATE_BASH: true
VALIDATE_GITHUB_ACTIONS: true
VALIDATE_MARKDOWN: true
VALIDATE_TERRAFORM_TFLINT: true
VALIDATE_YAML: true
DEFAULT_BRANCH: main

Issue reference

The issue this PR will close: #398

Checklist

Please make sure you've completed the relevant tasks for this PR out of the following list:

• All acceptance criteria in the backlog item are met
• The documentation is updated to cover any new or changed features
• Manual tests have passed
• Relevant issues are linked to this PR