Summary:
1. Added a new test to backup & restore ROLEs.
The new test uses `testPgRegressStyleUtil()` function.
2. The function was updated - one more hook was added to apply one more *.sql file
after the backup-create command & before the backup-restoring.
3. For other tests which are using the same function `testPgRegressStyleUtil()` I
moved all used *.sql/*.out/*.dump files into a separate new folder `src/postgres/src/test/regress/backup`.
It affects these 2 available tests: `testBackupRoleParameter` & `testPgRegressStyle`.
Jira: DB-18387

Test Plan:
New test:
./yb_build.sh --java-test org.yb.pgsql.TestYbBackup#testBackupRoles
./yb_build.sh --no-ybc --java-test org.yb.pgsql.TestYbBackup#testBackupRoles

Related updated tests:
./yb_build.sh --java-test org.yb.pgsql.TestYbBackup#testBackupRoleParameter
./yb_build.sh --no-ybc --java-test org.yb.pgsql.TestYbBackup#testBackupRoleParameter
./yb_build.sh --java-test org.yb.pgsql.TestYbBackup#testPgRegressStyle
./yb_build.sh --no-ybc --java-test org.yb.pgsql.TestYbBackup#testPgRegressStyle

Reviewers: sanketh, vkumar, dshubin, kfranz, #db-approvers

Reviewed By: kfranz

Subscribers: svc_phabricator, yguan, yql

Differential Revision: https://phorge.dev.yugabyte.com/D46870