[YSQL] Backups: Add new ROLEs related flags

[OlegLoginov]

Jira Link: DB-9947

Description

As it's discussed in the design doc the new flags must be added into the yb_backup.py scripts:
--backup_roles
--restore_roles
--ignore_existing_roles
--use_roles
The last flag should be passed into ysqlsh -v use_roles=true ....
In the YSQL dump should be implemented the new logic:

\if :{?use_roles}
\else
\set use_roles false
\endif

\if :{?ignore_existing_roles}
\else
\set ignore_existing_roles false
\endif

\if :ignore_existing_roles
IF EXISTS (SELECT 1 FROM pg_roles WHERE spcname = 'u2') THEN
     RAISE NOTICE 'User % already exists.', 'u2';
ELSE
     CREATE ROLE u2 ...
END IF;
\elif
CREATE ROLE u2 ...
\endif
...
-- Set privileges on t1
\if :use_roles
ALTER TABLE public.t1 OWNER TO u2;
GRANT SELECT ON TABLE public.t1 TO u2;
\endif

Issue Type

kind/new-feature

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