[MNG-7857] Introduce excplicit validation and documentation for Maven Coordinates

**[Tamas Cservenak](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cstamas)** opened **[MNG-7857](https://issues.apache.org/jira/browse/MNG-7857?redirect=false)** and commented

Some code (probably in model-builder validator?) that _excplicitly validates_ and self explains what which coordinate may look like. Examples: if you google, multiple users are asking "how is classifier' validated, and we (silently) imply classifer should not contain dot, but am unsure is it anywhere document and is it anywhere enforced/validated.

Or, if am wrong (and classifier is expected to contain dot), where is that documented?

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Some places where we could add these:
https://maven.apache.org/repositories/artifacts.html#artifact-properties
https://maven.apache.org/guides/mini/guide-naming-conventions.html

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