feat: add migration to move old files to xdg directory

+ add db column for migration version
+ handle pre-init migrations
+ handle post-init migration

app/migrations/_preinit/__init__.py

@@ -0,0 +1,38 @@
+"""
+Pre-init migrations are executed before the database is created.
+Useful when you need to move files or folders before the database is created.
+
+PLEASE NOTE: OLDER MIGRATIONS CAN NEVER BE DELETED.
+ONLY MODIFY OLD MIGRATIONS FOR BUG FIXES OR ENHANCEMENTS ONLY.
+[TRY NOT TO MODIFY BEHAVIOR, UNLESS YOU KNOW WHAT YOU'RE DOING].
+"""
+from sqlite3 import OperationalError
+
+from app.db.sqlite.migrations import MigrationManager
+from app.logger import log
+
+from .move_to_xdg_folder import MoveToXdgFolder
+
+all_preinits = [MoveToXdgFolder]
+
+
+def run_preinit_migrations():
+    """
+    Runs all pre-init migrations.
+    """
+    try:
+        userdb_version = MigrationManager.get_preinit_version()
+    except (OperationalError):
+        userdb_version = 0
+
+    for migration in all_preinits:
+        if migration.version > userdb_version:
+            log.warn("Running new pre-init migration: %s", migration.name)
+            migration.migrate()
+
+
+def set_preinit_migration_versions():
+    """
+    Sets the migration versions.
+    """
+    MigrationManager.set_preinit_version(all_preinits[-1].version)