Add Custom Username Support for Redis Connection in PgSync

[AbhiProjects]

This new feature allows users to specify a custom username for the Redis connection in PgSync. Previously, PgSync relied solely on the default Redis user. With this update, users can now provide their own Redis username, enhancing flexibility and security. One can provide the username via REDIS_USER environment variable.

[toluaina]

I see that Redis's user name is only supported by Redis 6 onwards.
So we need to modify this further to be backward compatible.
I will merge this and make the necessary changes, including adding tests. many thanks

[toluaina]

looks good.