feat(redis-v5/pg-v5): Update Redis/PG maintenance commands to suggest Data Maintenance CLI

[iriberri]

The Data Maintenance CLI (https://devcenter.heroku.com/articles/data-maintenance-cli-commands) was released a while ago and we want to recommend customers to switch to these new maintenance commands instead, which require the installation of an extra plugin.

This PR includes those changes for each of the maintenance-related commands for both Redis and Postgres add-ons on Heroku.

We will be making a few other changes from the Data side as well to match this. I expect this to be a short/medium-term change while we work towards deprecating the old commands.

The texts have been reviewed/suggested by CX already. I tried adapting to the existing content and tests but I'm really not very familiarised with JS neither how we develop for the CLI specially. If there's anything I need to adjust or any best practices I should be following, please, let me know!

Thank you.

cc: @jbrown-heroku (Product), @heicheng18 (CX)