Ability to replace domain zone record when it's the same type

[folfix]

Hi! I use ovh_domain_zone_record resource and I'd appreciate the option to override DNS record. Currently ovh_domain_zone_record's default behavior is to create new DNS record every time. Proposed solution is to introduce an argument (i.e. override) which will consider zone, subdomain and fieldtype and if there is already such record, it will just override (update) target.

Thanks for your effort!