fix: consent cockroachdb perfomance issue with zigzag join query (#1790)

Add an index over subject and client_id in order to avoid the
(sometimes) underperformant zigzag join query.

Closes #1789

Related to #1755 cockroachdb/cockroach#47179

persistence/sql/migrations/20200521071434_consent.cockroach.down.sql

@@ -0,0 +1 @@
+DROP INDEX hydra_oauth2_consent_request@hydra_oauth2_consent_request_client_id_subject_idx;

persistence/sql/migrations/20200521071434_consent.cockroach.up.sql

@@ -0,0 +1 @@
+CREATE INDEX hydra_oauth2_consent_request_client_id_subject_idx ON hydra_oauth2_consent_request (client_id, subject);

persistence/sql/migrations/20200521071434_consent.mysql.down.sql

@@ -0,0 +1 @@
+DROP INDEX hydra_oauth2_consent_request ON hydra_oauth2_consent_request_client_id_subject_idx;

persistence/sql/migrations/20200521071434_consent.mysql.up.sql

@@ -0,0 +1 @@
+CREATE INDEX hydra_oauth2_consent_request_client_id_subject_idx ON hydra_oauth2_consent_request (client_id, subject);

persistence/sql/migrations/20200521071434_consent.postgres.down.sql

@@ -0,0 +1 @@
+DROP INDEX hydra_oauth2_consent_request_client_id_subject_idx;

persistence/sql/migrations/20200521071434_consent.postgres.up.sql

@@ -0,0 +1 @@
+CREATE INDEX hydra_oauth2_consent_request_client_id_subject_idx ON hydra_oauth2_consent_request (client_id, subject);