Add redis to install scripts

[m4dcoder]

The coordinator service is required in most cases for running workflows. Install redis-server and configure redis as the default coordinator backend used by tooz. This will avoid a number of workflow issues, especially for new StackStorm users.

[m4dcoder]

This PR pairs with https://github.com/StackStorm/st2/pull/5226.

[arm4b]

Looks good :+1:

We'll also need to include Redis in CI, Tests and docker-compose:

• https://github.com/StackStorm/st2-packages/blob/master/docker-compose.override.yml
• https://github.com/StackStorm/st2-packages/blob/master/docker-compose.yml
• https://github.com/StackStorm/st2-packages/blob/master/docker-compose.circle2.yml
• https://github.com/StackStorm/st2-packages/blob/master/docker-compose.circle.yml
• https://github.com/StackStorm/st2-packages/blob/master/scripts/generate_st2_config.sh
• https://github.com/StackStorm/st2-packages/blob/master/rake/spec/default/60-st2_all-services-ok_spec.rb#L8-L11

[Kami]

As @armab said, LGTM, just need to make sure we update all other affected places (sadly there are quite a lot of those and some of those we will only stumble upon in the future - e.g. st2web also uses docker compose setup for end to end tests, etc.).