Query builder (#10104)

* add query builder to facilitate dynamic SQL construction

* leverage query builder to refactor user store

This is partially setup work for MM-13120, but merged to master to avoid
further conflicts.

* fix unrelated unit test breakage

* documentation tweaks

* Apply suggestions from code review

Co-Authored-By: lieut-data <jesse.hallam@gmail.com>

* prefer comma separated case options to fallthrough

* vendor github.com/Masterminds/squirrel and deps

* switch to using github.com/Masterminds/squirrel

* rm querybuilder

vendor/github.com/Masterminds/squirrel/row.go

@@ -0,0 +1,22 @@
+package squirrel
+
+// RowScanner is the interface that wraps the Scan method.
+//
+// Scan behaves like database/sql.Row.Scan.
+type RowScanner interface {
+	Scan(...interface{}) error
+}
+
+// Row wraps database/sql.Row to let squirrel return new errors on Scan.
+type Row struct {
+	RowScanner
+	err error
+}
+
+// Scan returns Row.err or calls RowScanner.Scan.
+func (r *Row) Scan(dest ...interface{}) error {
+	if r.err != nil {
+		return r.err
+	}
+	return r.RowScanner.Scan(dest...)
+}