githubscm PR-related methods need gh CLI

[jstastny-cz]

If a jenkinsfile uses methods like

• createPR*
• executeGHCli
• forkRepo
• approvePR
• mergePR
• createRelease*
• deleteRelease*
• isReleaseExist
• updateReleaseBody

it needs to have gh CLI binary on PATH, meaning it should use the kogito-ci-build image instead of ubuntu label in jenkins.

[jstastny-cz]

@cimbalek I don't know why often I assign you by mistake, disregard this one please.