Add 'contents: read' to workflow permissions to increase the OpenSSF scorecard of the repo

[pavlofilatov1]

Proposed Changes

These changes are being introduced to increase the repository's score that is calculated by the OpenSSF Scorecard (GitHub repo) tool.

This Pull Request updates the top-level permissions configuration within repo's GitHub workflows. It sets the default contents permission to read for the workflow token. The changes were done according to the recommendations from Scorecard regarding the token permissions and the discussion of this repository.

Types of Changes

Marked it as Other, but it is not the best choice. I would appreciate a recommendation regarding the right type.

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)
• Other

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[lukebakken]

@pavlofilatov1 thanks. Ping me when this is ready for review.