Issue #3533084: Replace Range constraint with PositiveOrZero for SMTP option fields
This merge request addresses issue #3533084 by updating the following integer fields in core.data_type.schema.yml that were using the Range constraint with only min: 0:
- restart_threshold
- restart_threshold_sleep
- ping_threshold
- max_per_second
These are now replaced with the more expressive PositiveOrZero constraint, as per the improvement introduced in #2853054.