feat: add options to override command and args

[Lowaiz]

We are running Renovate on few thousand repositories on a self-hosted Gitlab, and time to time, Gitlab produce a 429 return status code when POST/PUT a merge request, making a Renovate returning a non-zero code.

We don't really mind these fails, as it appears 2 or 3 times per run and renovate run twice a day.
But the set -e option let the cronjob as fail for Kubernetes, making it to be re run instantly, spamming the resources, without repeating the error on the same repo/branch.
So I propose to have an option to override the whole command and args part, to be able to override the set -e options

[Lowaiz]

@viceice
Hello,

Here is the full override implem, asked in #1299.
I have a little doubt about the precedence to apply between commandOverride/argsOverride and the preCommand/postCommand options.
In the format, you can:

• Override only the command, leaving empty args.
• Override only the args, leaving the custom Renovate command: renovate. so permitting the addition of args to this command.
• Override both for custom behavior.
• No override and usage of pre and postCommand, to have no breaking change.

[Lowaiz]

And for the naming of these options, I chose to use Override as it's already the case of few other options: nameOverride, fullNameOverride, ...

[viceice]

related

• Add unit tests #1341