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/V056__sql_admins_table.sql

@@ -0,0 +1,18 @@
+--
+-- Adds the ss13_admins SQL table again.
+--
+
+CREATE TABLE `ss13_admins` (
+  `ckey` VARCHAR(50) NOT NULL,
+  `rank` TEXT NOT NULL,
+  `flags` INT NOT NULL,
+  `status` TINYINT NOT NULL DEFAULT 1,
+  PRIMARY KEY (`ckey`),
+  CONSTRAINT `FK_ss13_admins_ss13_player_ckey` FOREIGN KEY(`ckey`) REFERENCES  `ss13_player` (`ckey`) ON UPDATE CASCADE
+) ENGINE=InnoDB COLLATE='utf8mb4_unicode_ci';
+
+ALTER TABLE `ss13_player`
+  DROP COLUMN `rank`,
+  DROP COLUMN `flags`;
+
+DROP TABLE `ss13_admin_log`;