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/V011__Discord_webhooks.sql

@@ -0,0 +1,8 @@
+CREATE TABLE `ss13_webhooks` (
+  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+  `url` longtext NOT NULL,
+  `tags` longtext NOT NULL,
+  `mention` varchar(32),
+  `dateadded` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  PRIMARY KEY (`id`)
+);