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/V052__setup_bg.sql

@@ -0,0 +1,6 @@
+--
+-- Adds support for character setup backgrounds in #9300
+-- 
+
+ALTER TABLE `ss13_characters`
+	ADD COLUMN `bgstate` VARCHAR(20) NULL DEFAULT NULL COLLATE 'utf8mb4_unicode_ci' AFTER `accent`;