feat!: internalChecksAsSuccess (#20572)

Adds new config option `internalChecksAsSuccess`, defaulting to `false`.

Closes #7800

BREAKING CHANGE: Internal checks such as `renovate/stability-days` will no longer count as passing/green, meaning that actions such as `automerge` won't
occur if the only checks are Renovate internal ones. Set `internalChecksAsSuccess=true` to restore existing behavior.