feat: add ddev redis alias, add ddev redis-flush, set empty password

[stasadev]

The Issue

ddev/ddev-redis-7 has command ddev redis, we can add an alias for this.

Also, there is a ddev redis-flush command in ddev/ddev-redis-7.

How This PR Solves The Issue

• Adds the mentioned commands.
• Explicitly sets an empty password (by default it is empty).

Manual Testing Instructions

ddev add-on get https://github.com/ddev/ddev-redis/tarball/20250425_stasadev_commands
ddev restart
ddev redis INFO
ddev redis-cli INFO
ddev redis-flush

Automated Testing Overview

Release/Deployment Notes