Rename methods called "service" to "integration"

This is part of &2504 (closed) to rename Service to Integration.

After changing the Service class to Integration #201848 (closed) we're left with a number of methods (mostly in Integration and Project, but likely elsewhere) that refer to these objects as "services" in both method names and variable names.

To complete the rename, we should also refactor these methods (and their variables) to refer to these objects as "integrations".