Add Postgres sql for JDBC implementation of OAuth2AuthorizedClientService

Postgres doesn't have a BLOB type, but it does have an equivalent BYTEA
type.
This approach and naming convention follows the convention established
in Spring Session JDBC which has sql for each RDBMS with files names in
the pattern *-{dbname}.sql, for example:
schema-db2.sql
schema-derby.sql
schema-h2.sql
schema-mysql.sql
schema-postgresql.sql

See https://github.com/spring-projects/spring-session/tree/2.3.1.RELEASE/spring-session-jdbc/src/main/resources/org/springframework/session/jdbc

Issue gh-9070

oauth2/oauth2-client/src/main/resources/org/springframework/security/oauth2/client/oauth2-client-schema-postgres.sql

@@ -0,0 +1,13 @@
+CREATE TABLE oauth2_authorized_client (
+  client_registration_id varchar(100) NOT NULL,
+  principal_name varchar(200) NOT NULL,
+  access_token_type varchar(100) NOT NULL,
+  access_token_value bytea NOT NULL,
+  access_token_issued_at timestamp NOT NULL,
+  access_token_expires_at timestamp NOT NULL,
+  access_token_scopes varchar(1000) DEFAULT NULL,
+  refresh_token_value bytea DEFAULT NULL,
+  refresh_token_issued_at timestamp DEFAULT NULL,
+  created_at timestamp DEFAULT CURRENT_TIMESTAMP NOT NULL,
+  PRIMARY KEY (client_registration_id, principal_name)
+);