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

config/store_test.go

@@ -0,0 +1,35 @@
+package config_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/mattermost/mattermost-server/config"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewStore(t *testing.T) {
+	t.Run("database dsn", func(t *testing.T) {
+		ds, err := config.NewStore(fmt.Sprintf("%s://%s", *mainHelper.Settings.DriverName, *mainHelper.Settings.DataSource), false)
+		require.NoError(t, err)
+		ds.Close()
+	})
+
+	t.Run("database dsn, watch ignored", func(t *testing.T) {
+		ds, err := config.NewStore(fmt.Sprintf("%s://%s", *mainHelper.Settings.DriverName, *mainHelper.Settings.DataSource), true)
+		require.NoError(t, err)
+		ds.Close()
+	})
+
+	t.Run("file dsn", func(t *testing.T) {
+		fs, err := config.NewStore("config.json", false)
+		require.NoError(t, err)
+		fs.Close()
+	})
+
+	t.Run("file dsn, watch", func(t *testing.T) {
+		fs, err := config.NewStore("config.json", true)
+		require.NoError(t, err)
+		fs.Close()
+	})
+}