Database: Add *sort fields, bpm, mood, initial_key

Upgrade from schema version 20 to 21. This includes:

- six fields for sort tags
- new fields bpm, mood, initial_key

See https://github.com/strawberrymusicplayer/strawberry/pull/1779#pullrequestreview-3003042802

src/device/devicedatabasebackend.cpp

@@ -41,7 +41,7 @@
 using namespace Qt::Literals::StringLiterals;
 
 namespace {
-constexpr int kDeviceSchemaVersion = 5;
+constexpr int kDeviceSchemaVersion = 6;
 }
 
 DeviceDatabaseBackend::DeviceDatabaseBackend(QObject *parent)