Use `main` as primary branch

[lemeurherve]

Suggestion

We should use main instead of master as primary branch.

This will need updating not only this repo but also all references to master in Jenkinsfile(s) and job on ci.jenkins.io, infra.ci.jenkins.io, release.ci.jenkins.io and trusted.ci.jenkins.io (not sure about cert.ci.jenkins.io), and changing settings of Jenkins instances around global shared pipeline library.

Links

• https://github.com/jenkins-infra/helpdesk/issues/2671

[lemeurherve]

Also be wary that this pipeline library is referenced in multiples repositories, a global search across them will be needed to ensure all references are updated.