GitHub Workflows security hardening

[sashashura]

This PR adds explicit permissions section to workflows. This is a security best practice because by default workflows run with extended set of permissions (except from on: pull_request from external forks). By specifying any permission explicitly all others are set to none. By using the principle of least privilege the damage a compromised workflow can do (because of an injection or compromised third party tool or action) is restricted.
It is recommended to have most strict permissions on the top level and grant write permissions on job level case by case.

[gnidan]

Thanks for this! And for going through and shepherding this same change on so many widely-used projects!

[haltman-at]

What does contents actually cover? I'm having trouble finding documentation on this.

[sashashura]

What does contents actually cover? I'm having trouble finding documentation on this.

Here is the mapping of GitHub app contents to api calls. This is the best I can find, otherwise it is not documented.

[cds-amal]

Thanks for this!