Refactor shell scripts

[stefaniuk]

Description

This is the first part of the refactoring effort to ensure that the shell scripts:

• Follow a consistent convention,
• Pass the ShellCheck linting test (please run make shellscript-lint-all), and
• Work either with the pre-installed CLI tooling or run commands using Docker containers.

Context

Information for a reviewer:

• The first two commits, a4517db and 7b94f14, implement stylistic and linting recommendations.
• The last two commits, f8b9e84 and 22f7700, refactor how tools like Gitleaks and SonarScanner are executed.

Type of changes

• [x] Refactoring (non-breaking change)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would change existing functionality)
• [ ] Bug fix (non-breaking change which fixes an issue)

Checklist

• [x] I am familiar with the contributing guidelines
• [x] I have followed the code style of the project
• [ ] I have added tests to cover my changes
• [ ] I have updated the documentation accordingly
• [ ] This PR is a result of pair or mob programming

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Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

• [x] I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.