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/doc.go

@@ -0,0 +1,12 @@
+// Package sqlx provides general purpose extensions to database/sql.
+//
+// It is intended to seamlessly wrap database/sql and provide convenience
+// methods which are useful in the development of database driven applications.
+// None of the underlying database/sql methods are changed.  Instead all extended
+// behavior is implemented through new methods defined on wrapper types.
+//
+// Additions include scanning into structs, named query support, rebinding
+// queries for different drivers, convenient shorthands for common error handling
+// and more.
+//
+package sqlx