docs(DB): Database Squash (#19415)

data/sql/base/database-squash.md

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+New routines around handling database squashes since https://github.com/azerothcore/azerothcore-wotlk/pull/18197
+
+> [!CAUTION]
+> These steps are only for project maintainers who intend to update base files.
+
+We ONLY squash into BASE files. We never move files.
+ARCHIVE dir is UNUSED.
+All update files ALWAYS exist in the updates dir.
+
+as the `updates` table in base files always will contain the entries from the updates dir they will never be run again on a clean setup. 
+
+How to do the squash.
+
+> [!IMPORTANT]
+> A squash needs to be done on a clean database. Drop all tables in Auth, Characters and World.
+
+1. Update the acore.json file. Increment version by one
+2. Create a new file in the updates/db_world/ dir, the file should be incremented containing
+
+> [!NOTE]
+> It should NOT be placed as a pending update and should only be done on world db. This is because we want the updated DB version to follow into the base files
+
+```sql
+UPDATE `version` SET `db_version`='ACDB 335.11-dev', `cache_id`=11 LIMIT 1;
+```
+> [!NOTE]
+> Remember to increment the db_version and cache_id the same as acore.json
+
+4. Drop all your databases, and run Worldserver to populate a clean database.
+5. Export the databases using i.e HeidiSQL
+
+> [!IMPORTANT]
+> Set the following values
+> Tables -> DROP + CREATE
+> Data -> Delete + insert (truncate existing data)
+> Max INSERT size -> 1024
+> This is so that no unexpected issues occur.
+
+6. Move the exported table files into the base directory to update the existing files.
+7. Make a PR