Postgres/MySQL/MSSQL: Add setting to limit maximum amount of rows processed (#38986)

Adds a new setting dataproxy.row_limit that allows an operator to limit the 
amount of rows being processed/accepted in response to database queries 
originating from SQL data sources.

Closes #38975
Ref #39095

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

pkg/setting/setting.go

@@ -327,6 +327,7 @@ type Cfg struct {
 	DataProxyKeepAlive             int
 	DataProxyIdleConnTimeout       int
 	ResponseLimit                  int64
+	DataProxyRowLimit              int64
 
 	// DistributedCache
 	RemoteCacheOptions *RemoteCacheOptions