SQLStore: customise the limit of retrieved datasources per organisation (#29358)

* SQLStore: customise the limit of retrieved datasources per organisation

* update all suggestions regarding nil or 0 as default

* Apply suggestions from code review

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>

* correct default.ini description + adding unittest

* Apply suggestions from code review

Co-authored-by: Sofia Papagiannaki <papagian@users.noreply.github.com>

* modify unittest name

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>
Co-authored-by: Sofia Papagiannaki <papagian@users.noreply.github.com>

pkg/services/sqlstore/sqlstore.go

@@ -354,7 +354,7 @@ func (ss *SQLStore) readConfig() {
 	ss.dbCfg.CacheMode = sec.Key("cache_mode").MustString("private")
 }
 
-// Interface of arguments for testing db
+// ITestDB is an interface of arguments for testing db
 type ITestDB interface {
 	Helper()
 	Fatalf(format string, args ...interface{})