[MRESOLVER-625] Rewrite homepage to reflect new resolver provider location in Maven4

**[Konrad Windszus](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=kwin)** opened **[MRESOLVER-625](https://issues.apache.org/jira/browse/MRESOLVER-625?redirect=false)** and commented

The page at https://github.com/apache/maven-resolver/blob/maven-resolver-2.0.3/src/site/xdoc/index.xml still refers to a dedicated Maven 3 module. With Maven4 this dissolved and is now part of https://github.com/apache/maven/tree/master/impl/maven-impl. Would be good to adjust links and provide proper entry points.

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**Issue Links:**
- [MRESOLVER-626](https://issues.apache.org/jira/browse/MRESOLVER-626) Rewrite homepage to reflect new resolver provider location in Maven4
(_**"is duplicated by"**_)

Start with src/site/xdoc/index.xml and compare its Maven 3 module references with the Maven 4 location at impl/maven-impl. Update the homepage links and entry points so they reflect the new resolver provider location; it is done when the page no longer points to the dissolved dedicated module.

Written by the indexing model from the issue text.