adding timeout attribute to function node

- [x] New feature (non-breaking change which adds functionality)

Discussion here:
https://discourse.nodered.org/t/function-node-doesnt-have-timeout-feature/78483

## Proposed changes

Adding a timeout attribute to the function node, so an endless funciton doesnt break the node red server.

## Checklist

- [x] I have read the [contribution guidelines](https://github.com/node-red/node-red/blob/master/CONTRIBUTING.md)
- [x] For non-bugfix PRs, I have discussed this change on the forum/slack team.
- [x] I have run `grunt` to verify the unit tests pass
- [x] I have added suitable unit tests to cover the new/changed functionality

test/nodes/core/function/10-function_spec.js

@@ -1424,7 +1424,30 @@ describe('function node', function() {
         });
     });
 
-
+    it('should timeout if timeout is set', function(done) {
+        var flow = [{id:"n1",type:"function",wires:[["n2"]],timeout:"10",func:"while(1==1){};\nreturn msg;"}];
+        helper.load(functionNode, flow, function() {
+            var n1 = helper.getNode("n1");
+            n1.receive({payload:"foo",topic: "bar"});
+            setTimeout(function() {
+                try {
+                    helper.log().called.should.be.true();
+                    var logEvents = helper.log().args.filter(function(evt) {
+                        return evt[0].type == "function";
+                    });
+                    logEvents.should.have.length(1);
+                    var msg = logEvents[0][0];
+                    msg.should.have.property('level', helper.log().ERROR);
+                    msg.should.have.property('id', 'n1');
+                    msg.should.have.property('type', 'function');
+                    should.equal(msg.msg.message, 'Script execution timed out after 10ms');
+                    done();
+                } catch(err) {
+                    done(err);
+                }
+            },50);
+        });
+    });
 
     describe("finalize function", function() {