adding an optional "additionalConstraints" multi-line text attribute on resources ad resourceProperties.

[jadelkhoury]

Description

adding an optional "additionalConstraints" multi-line text attribute on resources ad resourceProperties.

Checklist

• [x] This PR adds an entry to the CHANGELOG. _See https://keepachangelog.com/en/1.0.0/ for instructions. Minor edits are exempt.
• [ ] This PR expects some manual changes to the generated code. The needed changes are detailed in the CHANGELOG entry.
• [x] This PR was tested with at least one code generation, resulting in a working OSLC server.
• [x] This PR does NOT break the user block code

[jadelkhoury]

This overrides https://github.com/eclipse/lyo.designer/pull/240 which will be closed.

[jadelkhoury]

Reviewed and approved together with @berezovskyi