As part of the effort to rename "services" to "integrations" throughout
the codebase, this duplicates the REST API routes so that it is available
under both the `/services` and `/integrations` endpoints.

Changelog: changed
Co-authored-by: Andy Soiron <asoiron@gitlab.com>
Co-authored-by: Luke Duncalfe <lduncalfe@gitlab.com>
Co-authored-by: Markus Koller <mkoller@gitlab.com>