Add PostgreSQL backend

[leso-kn]

This PR adds experimental PostgreSQL support.

Based upon the work of @dxtr, extended and adapted to the latest version of Baikal.

✅ The following features were tested:

• Baikal setup procedure / UI (with Postgres)
• Creating / deleting / editing a user
• Creating / deleting / editing a calendar
• Listing contacts
• Logging in / creating / deleting an event through the webui (User login)
• Subscribing to a calendar / adding / deleting an event through a DAV client
  • Thunderbird
  • DAVx⁵ for Android

[leso-kn]

ref #122

[2Belette]

since one ! does this PR would make it into new release ?

[comrada]

Looking forward to Postgresql support!! I keep MySQL on the server just for the sake of Baikal.

[ndruba]

I use Baikal with this patch for my personal use during half year from clean install and don't have any troubles.

The following features were tested:

Baikal setup procedure / UI (with Postgres) Creating a user Creating / editing a calendar (with Todos and Tasks) Creating / editing Address Book Logging in, listing an event and contacts through the webui (dav.php) Subscribing to a calendar and address book / adding / deleting an event and contacts through a DAV client Thunderbird Carddav-sync/Caldav-sync

[leso-kn]

@Terrance Done! Sorry for the late reply, the updates described in your previous comment are now included in 54ebfe0

[dewey]

Great to see this, any idea what would be needed to get this merged?

[PrivatePuffin]

Combined with CloudNative-PG this finally gives an easy route to enterprise-grade hosted baikal, nice!

[nileshtrivedi]

Looking forward to this being merged that would finally fix #122