Config UI: add tariffs (#26698)

Co-authored-by: Maschga <88616799+Maschga@users.noreply.github.com>
Co-authored-by: andig <cpuidle@gmail.com>
Co-authored-by: andig <andi@evcc.io>

tests/tariffs-legacy.sql

@@ -0,0 +1,8 @@
+CREATE TABLE IF NOT EXISTS `settings` (
+    `key` text
+  , `value` text
+  , PRIMARY KEY(`key`)
+);
+
+-- legacy tariff configuration stored in database
+INSERT INTO settings("key", value) VALUES('tariffs', 'currency: EUR');