[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).

Inizia da plugin-maven/README.md e rivedi gli esempi di plugin esistenti. Documenta le coordinate Maven per ogni plugin e includi un URL alternativo per gli strumenti senza artefatti Maven; consulta l’issue 1922 per il contesto greclipse a cui si fa riferimento. Il lavoro è completato quando il README espone le coordinate o un URL di versione utilizzabile per ogni esempio.

Scritto dal modello di indicizzazione a partire dal testo della issue.