[Task]: Renew Data Retention policy doc

[KevinMind]

Description

Based on our existing data retention policy document lets rewrite adding or updating with the following focus:

• Define terms such as "deletion" "account" "user data" very clearly
• Define the mechanism of deletion and high level how it works
• Update the dates for retention:
  • user that has not logged in in over 2 years and has no user data should be deleted
  • user that has not logged in in over 7 years and has "safe to delete" user data should be deleted

This doc can be used to align our goals in terms of data retention and after complete and approved across our stakeholders we can integrate it into our addons-server docs site for future git proofing updates and eventually implement logic to ensure our actual data cleaning jobs are working as expected.

NEW DATA RETENTION POLICY

Checks

• [x] If I have identified that the work is specific to a repository, I have removed "repository:addons-server" or "repository:addons-frontend"

┆Issue is synchronized with this Jira Task

[diox]

We need that doc before end of March to get it circulated to the right people.