Persist groupnodes and sticky notes

[Daan0709]

• Flow:x and flow:y attributes now get rounded
• Sticky notes now get persisted
• Group nodes now get persisted
• They get stored inside a new <flow:FlowElements> element so they can be directly stored within the configuration xml, directly underneath the pipeline:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Daan0709]

@Matthbo Could you take a look at how this is implemented right now? Because of my inexperience with xml I am uncertain if storing the flowelements like this will cause any issues with Configurations or if they will get ignored because of the flow namespace prefixed to it. It would seem that the xsd is picking up on it and flagging it as wrong (as you can see in the screenshot in the title of this PR). I am also wondering if you perhaps had a more elegant solution overall.