Add the service role to ironic service users. Ironic recently enforced
new policy validation as part of the RBAC efforts. [1][2]
Service user support was also added to Ironic. [3]
Admin role needs to stay as not all services added service role support. [4][5]

[1] https://review.opendev.org/c/openstack/ironic/+/902009
[2] https://opendev.org/openstack/governance/src/commit/e2a47de10a689a78c31765fd1b020f17c0d3109c/goals/selected/consistent-and-secure-rbac.rst#phase-2
[3] https://review.opendev.org/c/openstack/ironic/+/907148
[4] https://review.opendev.org/q/topic:bp%252Fpolicy-service-role-default
[5] https://review.opendev.org/q/topic:%22New-Location-Apis%22

Related-Bug: #2051837
Change-Id: I048402c2247188cf57f35437f557f84ac25d4ff2