Don't rev namespace with each release

### Affected version

HEAD and many previous versions

### Bug description

The current setup is creating new namespaces for each release. E.g.

```
https://maven.apache.org/xsd/assembly-2.2.0.xsd, https://maven.apache.org/xsd/assembly-component-2.2.0.xsd (for version 3.6.0 and higher)
https://maven.apache.org/xsd/assembly-2.1.1.xsd, https://maven.apache.org/xsd/assembly-component-2.1.1.xsd (for version 3.4.0 and higher)
https://maven.apache.org/xsd/assembly-2.1.0.xsd, https://maven.apache.org/xsd/assembly-component-2.1.0.xsd (for version 3.2 and higher)
https://maven.apache.org/xsd/assembly-2.0.0.xsd, https://maven.apache.org/xsd/assembly-component-2.0.0.xsd (for version 3.0 and higher)
https://maven.apache.org/xsd/assembly-1.1.3.xsd, https://maven.apache.org/xsd/component-1.1.3.xsd (for version 2.5.4 and higher)
https://maven.apache.org/xsd/assembly-1.1.2.xsd, https://maven.apache.org/xsd/component-1.1.2.xsd (for version 2.2 and higher)
https://maven.apache.org/xsd/assembly-1.1.1.xsd, https://maven.apache.org/xsd/component-1.1.1.xsd (for version 2.2-beta-4 - 2.2-beta-5)
https://maven.apache.org/xsd/assembly-1.1.0.xsd, https://maven.apache.org/xsd/component-1.1.0.xsd (for version 2.2-beta-1 - 2.2-beta-3)
https://maven.apache.org/xsd/assembly-1.0.0.xsd, https://maven.apache.org/xsd/component-1.0.0.xsd (for version 2.1 and lower)
```

I don't think that's a complete list, just what we currently document. This is not the purpose or intent of XML namespaces. Namespaces are not versions, and this approach breaks a lot of XML processing chains based on XPath, XQuery, XInclude, JDOM and/or XSLT among many others. There should be a single namespace that doesn't change unless we really redo everything from scratch with a new vocabulary.

The issue names no files, tests, or entry points. Begin by tracing where the documented assembly and component XML namespaces are declared, then establish the compatibility requirements; the work is done when releases use one stable namespace without disrupting existing XML processing.

Written by the indexing model from the issue text.