[Neutron] Speed up access to neutron resources by indexing RBAC database columns "target_tenant" and "action"

Issue

Two columns in the RBAC databases are referenced in queries but not indexed. This causes sub-optimal search performance.

Neutron provides role-based access control [2] to a set of resources (networks, QoS policies, security groups, address scopes, subnet pools and address groups). Each time those resources are requested using the Neutron API, the Neutron server performs a database request using the role ID of the user and the RBAC configuration for each resource. That triggers an SQL query like this one:

SELECT 
    networkrbacs.project_id AS networkrbacs_project_id,
    networkrbacs.id AS networkrbacs_id,
    networkrbacs.target_tenant AS networkrbacs_target_tenant,
    networkrbacs.action AS networkrbacs_action,
    networkrbacs.object_id AS networkrbacs_object_id,
    anon_1.networks_id AS anon_1_networks_id
FROM
    (SELECT 
        networks.id AS networks_id
    FROM
        networks
    LEFT OUTER JOIN networkrbacs ON networks.id = networkrbacs.object_id
    WHERE
        (networkrbacs.action = 'access_as_external'
            AND networkrbacs.target_tenant = 'd411a44c5fec4d4883e2648d1e34faf6'
            OR networkrbacs.target_tenant = '*'
            OR networks.project_id = 'd411a44c5fec4d4883e2648d1e34faf6'
            OR networkrbacs.action = 'access_as_shared'
            AND (networkrbacs.target_tenant = 'd411a44c5fec4d4883e2648d1e34faf6'
            OR networkrbacs.target_tenant = '*'))
            AND (EXISTS( SELECT 
                1
            FROM
                externalnetworks
            WHERE
                networks.id = externalnetworks.network_id))) AS anon_1
        INNER JOIN
    networkrbacs ON anon_1.networks_id = networkrbacs.object_id
ORDER BY anon_1.networks_idc

The issue with this SQL query is that currently no RBAC model indexes the "target_tenant" and "action" columns and the performance is suboptimal.

[2]https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/16.2/html/networking_guide/config-rbac-policies_rhosp-network