MM-11262: database config store (#10281)

* vendor github.com/jmoiron/sqlx

* MM-11262: introduce a database store

* revert unnecessary fmt.Errorf

* simplify unit test helper methods

* remote TODO re: retry

* relocate initializeConfigurationsTable for clarity

* factor out a commonStore

* acquire database config lock on close for safety

* add missing header

* fix lock comment

vendor/github.com/jmoiron/sqlx/go.mod

@@ -0,0 +1,7 @@
+module github.com/jmoiron/sqlx
+
+require (
+	github.com/go-sql-driver/mysql v1.4.0
+	github.com/lib/pq v1.0.0
+	github.com/mattn/go-sqlite3 v1.9.0
+)