Add support for properties (name-value pairs)

Schema 1.3 added support for [properties](https://cyclonedx.org/use-cases/#properties--name-value-store) (name-value pairs).

Now that Schema 1.3 is implemented in cyclonedx-maven-plugin as of v2.5.0, it would be useful for the plugin to support properties.

For maven projects in Dependency-Track, this enhancement would be the ying to the yang of [Add support for namespaced CDX custom properties for DT features](https://github.com/DependencyTrack/dependency-track/issues/1187)

Start by reading the plugin's existing Schema 1.3 implementation and the CycloneDX properties specification linked in the issue. Trace how Maven project data is represented in the generated BOM, then verify that name-value properties appear in the output for a Maven project.

Written by the indexing model from the issue text.