[ADR] Select a backup solution for Mattermost

[Racer159]

Is your feature request related to a problem? Please describe.

As Ashton I want to be able to backup Mattermost safely so that I can restore it easily in the event of a disaster.

Describe the solution you'd like

We should identify and select solutions that are able to backup the Mattermost database and critical files, and then follows the recommendations for restoration:

https://docs.mattermost.com/deploy/backup-disaster-recovery.html

These should be written in a simple ADR to capture why the final solution was chosen and a follow on implementation issue should be created.

Additional context

We currently don't have set SLAs but should target a baseline to have something while we continue to experiment.

[zachariahmiller]

Essentially, follow normal RDS backup/snapshot practices and also backup additional files as indicated here https://docs.mattermost.com/deploy/backup-disaster-recovery.html