Add redis engine version var

[brian-penguin]

Add a new variable for configuring redis engine version
Why this change is being made:

• New Sidekiq versions require at lease redis 7.3 to run. We have it
  hardcoded in this playbook at 6.x. I want to make it so we can change
  an env var and upgrade our Redis version

What were the changes made to support this:

• Add a new variable to the redis-variables.tf
• Set the default to 7.x
• use the variable in redis.tf

[brian-penguin]

@clarissalimab I've never worked with terraform directly before. Is there anything I'm missing? I am also not sure how to set the redis variable for us in the Hub application. Any advice?

[clarissalimab]

@brian-penguin I think you got everything right!

Once we merge this and tag a version, you can go to Hub's infrastructure configuration on thoughtbot-infra, and replace the version of the terraform-flightdeck-aws-application module with the new tag and run a terraform init and push the changes to a pull request. If the terraform plan looks good, the changes will be applied once we merge your PR on thoughtbot-infra.

I would at least test running a terraform init and terraform plan against these changes before merging them, if you can. To do this, instead of replacing the module version with the new tag, you would replace it with your latest commit hash or replace the module source entirely with the relative path to your local module directory.

[brian-penguin]

https://github.com/thoughtbot/thoughtbot-infra/pull/268