Which role would is MOST SUITABLE for someone with experience of managing relationships with various...

The purpose of the SLM practice is to set clear business-based targets for service performance, so that the delivery of a service can be properly assessed, monitored, and managed against these targets. SLM involves service level activities, including:

Defining service levels

Documenting

Actively managing them

https://www.bmc.com/blogs/itil-service-level-management/