[RFE][Docs] Publish g:a:v in maven-plugin-documentation

This is a recommendation / request for enhancement for https://github.com/diffplug/spotless/blob/main/plugin-maven/README.md.

## feature description

Please publish the Maven coordinates for every plugin.
E.g. palantir:

```xml

com.palantir.javaformat
palantir-java-format
2.38.0

```

## use case

### Users can easily find new versions

Users can use the coordinates and go to https://search.maven.org/ to see whether there are more recent versions, or older versions if needed.

### can be picked up by dependency bots

If you put the above into your dependency management, preferably using a property for the version, tools like renovate or dependabot can update the dependency.
With the current examples, those versions will never be picked up.

### can be scanned by security scanners

If you put the above into your dependency management, security scanners will recognise the artefact, too.

## versions without Maven artefacts

For tools like greclipse, publish another URL which can be used.
(optional) For greclipse specifically, show the Maven coordinates for the older versions (as mentioned in https://github.com/diffplug/spotless/issues/1922).

Beginne mit plugin-maven/README.md und überprüfe die vorhandenen Plugin-Beispiele. Dokumentiere die Maven-Koordinaten für jedes Plugin und füge eine alternative URL für Tools ohne Maven-Artefakte hinzu; sieh dir Issue 1922 wegen des referenzierten greclipse-Kontexts an. Als erledigt gilt die Aufgabe, wenn das README für jedes Beispiel Koordinaten oder eine nutzbare Versions-URL enthält.

Vom Indexierungsmodell aus dem Issue-Text verfasst.