Adds a new concept `logContext`, to be added to each log entry when in JSON format.

Closes #5551

New config option `rebaseWhen` replaces existing options `rebaseStalePrs` and `rebaseConflctedPrs`. Migration code added.

Co-authored-by: Rhys Arkins <rhys@arkins.net>

Co-authored-by: Dominik Horb <git@dominik.berlin>

This reverts commit edf85d42.

Closes #5121

Closes https://github.com/renovatebot/docs.renovatebot.com/issues/5

Closes https://github.com/renovatebot/docs.renovatebot.com/issues/6

Adds new `ignoreScripts` config option. If set to true, managers such as npm and composer will skip running install scripts even if trustLevel is configured to high.

Closes #4567

Adds options onboardingBranch and onboardingPrTitle to allow bot administrators to change the branch name and/or title in oboarding PRs.