Show product usage types in credit ledger

Persist hotword request origin so every reservation lifecycle entry can be classified without mutating the immutable ledger.

src/main/resources/db/migration/V14__provider_request_source.sql

@@ -0,0 +1,5 @@
+ALTER TABLE provider_requests
+    ADD COLUMN request_source VARCHAR(32) CHARACTER SET ascii COLLATE ascii_bin NULL AFTER capability,
+    ADD CONSTRAINT chk_provider_request_source CHECK (
+        request_source IS NULL OR request_source IN ('HOTWORD')
+    );