ci: Add GitHub token permissions for workflows

[varunsh-coder]

GitHub asks developers to define workflow permissions, see https://github.blog/changelog/2021-04-20-github-actions-control-permissions-for-github_token/ and https://docs.github.com/en/actions/security-guides/automatic-token-authentication#modifying-the-permissions-for-the-github_token for securing GitHub workflows against supply-chain attacks.

The Open Source Security Foundation (OpenSSF) Scorecards also treats not setting token permissions as a high-risk issue.

This PR adds minimum token permissions for the GITHUB_TOKEN using https://github.com/step-security/secure-workflows.

This project is part of the top 100 critical projects as per OpenSSF (https://github.com/ossf/wg-securing-critical-projects), so fixing the token permissions to improve security.

I am not sure if I need to create the JIRA issue for this. If I do, please let me know.

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[varunsh-coder]

Please let me know if there is anything pending on my side for this PR?

[slawekjaranowski]

@varunsh-coder Thanks for your effort, I did similar in #871