Switch to 6.0.0-SNAPSHOT

[Jad-el-khoury]

Description

Switch to 6.0.0-SNAPSHOT to match Lyo's versioning. Next step would be to generate code for Java 17.

Checklist

• [ ] 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.
• [ ] 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

[Jad-el-khoury]

@berezovskyi ! Just changing the version to 6.0.0-SNAPSHOT for LyoDesigner to match Lyo.