[Inactive Users] Redis configuration for user's login activity record

[Arsnael]

cf EPIC for context

For reporting a list of inactive users on the mail platform, we need to be able to record user's login activity somewhere.

Redis has been chosen as the most suitable storage for this need: famous for session data use case, fast write, AOF seems reasonable for data backup (could accept a bit of data lag for user activity use case).

regarding the way of storing data structure:

• the key can be something like: last-login:<username> where username is the actual user's last login info
• the value: a JSON that would have the last connection date, ip and user agent registered per protocol (imap, smtp). We would use Redis JSON.SET command

Example of the JSON value:

{
 "imap": {
   "lastConnectionDate": "XXXX",
   "ipAddress": "XXX",
   "userAgent": "XXX"
 },
 "smtp": {
   "lastConnectionDate": "XXXX",
   "ipAddress": "XXX",
   "userAgent": "XXX"
 }
}

Maybe create a new module under tmail-backend for this, like user-login-redis? (can discuss the name)

DoD

• Unit tests