Grant Overall/SystemRead to committers by default

[mbarbero]

It's GA since https://www.jenkins.io/changelog-stable/#v2.263.1 and we can now grant it to committers. I think it would be helpful for them.

[mbarbero]

I guess that we could also provide Job/ExtendedRead at the same time

[fredg02]

+1, I was planning to test it. It would be nice to have a test user account for that.

[mbarbero]

You don't necessarily need a test account. Change the permission on 1 instance where you grant the admin group the desired permissions and test from there. When you need the full god mode back, re-deploy with full administer perm to the admin group.