Apply templating on alert notifications on OK state (#47355)

* OK notifications using previous evaluation data

* copy rule.EvalMatches to avoid changes to the underlying array

* test cases added/modified

* delete trailing newline

* fix double newline in go import

* add change to the changelog

* specify that this only affects legacy alerting (changelog)

* use current eval data instead of prev eval data

* create evalMatch just once

* code comments, renamings, getTemplateMatches() function

* changelog and docs updated

pkg/services/alerting/eval_handler.go

@@ -68,6 +68,7 @@ func (e *DefaultEvalHandler) Eval(context *EvalContext) {
 		}
 
 		context.EvalMatches = append(context.EvalMatches, cr.EvalMatches...)
+		context.AllMatches = append(context.AllMatches, cr.AllMatches...)
 	}
 
 	context.ConditionEvals = conditionEvals + " = " + strconv.FormatBool(firing)