[ARCHETYPE-540] Upgrade from 2.x compatible archetype to 3.x document

**[Tim Pizey](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=timp)** opened **[ARCHETYPE-540](https://issues.apache.org/jira/browse/ARCHETYPE-540?redirect=false)** and commented

I had a nice archetype, I cannot discover how to make it work, nor can I go back to 2.x series. 

The move from 2 to 3 is breaking a change but there is no upgrade document.

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No further details from [ARCHETYPE-540](https://issues.apache.org/jira/browse/ARCHETYPE-540?redirect=false)

Start by reading the linked ARCHETYPE-540 report and the Apache Maven Archetype repository description to understand the 2.x-to-3.x compatibility break. No file or test is named, so identify the relevant upgrade steps and verify that the finished documentation explains how an existing 2.x-compatible archetype can work with 3.x.

Written by the indexing model from the issue text.