Condense Database Migrations (#17103)

* Condense Database Migrations

Condenses the Database Migrations into a new initial schema.
Also adds some instructions to the Database Readme for existing setups.

* Update readme/delete changed migrations since pr creation

* Reworks a bit how the previous migrations are handled and updates the instructions accordingly

* Expand the readme with baseline/migrate

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Co-authored-by: Werner <Arrow768@users.noreply.github.com>

SQL/migrate-2017/V024__poll_links.sql

@@ -0,0 +1,6 @@
+--
+-- Allows to add a link to the poll
+--
+
+ALTER TABLE `ss13_poll_question`
+  ADD COLUMN `link` VARCHAR(250) NULL DEFAULT NULL AFTER `createdby_ip`;