Add an option not to change bugs when max number of needinfo is reached

At the moment, for scripts that make some changes and needinfo someone, if you set a maximum number of needinfos after the number is reached the changes are still done but without the needinfo.

E.g. in the assignee_no_login script, if we use the default max_ni behavior from bzcleaner (with max_ni = 3) and we have 5 bugs to unassign in the same component, we'd do:
Bug 1 - Needinfo triage owner and mark bug as unassigned
Bug 2 - Needinfo triage owner and mark bug as unassigned
Bug 3 - Needinfo triage owner and mark bug as unassigned
Bug 4 - Mark bug as unassigned
Bug 5 - Mark bug as unassigned

What we want to do instead is only apply changes and needinfo in Bug 1, 2 and 3 and leave 4 and 5 for the next run.

To implement this, we could for example return early when auto_ni is None at https://github.com/mozilla/relman-auto-nag/blob/7b1a6038d926594463b68eb064f2323c196d149a/auto_nag/bzcleaner.py#L231.

Start in auto_nag/bzcleaner.py around line 231 and trace how auto_ni becomes None after the maximum needinfo count is reached. The change is complete when scripts skip both needinfo and other changes for later bugs, leaving them for the next run.