[MSITE-1015] Get rid of Wagon dependency

**[Konrad Windszus](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=kwin)** opened **[MSITE-1015](https://issues.apache.org/jira/browse/MSITE-1015?redirect=false)** and commented

As Maven Wagon is lacking maintenance and most of the sites leverage https://maven.apache.org/plugins/maven-scm-publish-plugin/ nowadays to deploy a site we should get rid of the Wagon dependency and support certain transport protocols directly:

1. GitHub Pages via https://docs.github.com/en/rest/pages/pages?apiVersion=2022-11-28#create-a-github-pages-deployment, the [ReST API for uploading the artifact is not documented](https://github.com/actions/upload-artifact/issues/180)
2. SCMs via https://maven.apache.org/scm/
3. SFTP via https://github.com/apache/mina-sshd/blob/master/docs/sftp.md

This would allow to get rid of one abstraction layer, improve error reporting and finally deprecate https://maven.apache.org/plugins/maven-scm-publish-plugin/.

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No further details from [MSITE-1015](https://issues.apache.org/jira/browse/MSITE-1015?redirect=false)

Start by locating the current Maven Wagon integration and understanding how site deployment is handled. Compare the requested GitHub Pages API, Maven SCM transports, and Apache Mina SFTP documentation; completion would remove the Wagon dependency while directly supporting the stated transport protocols and improving error reporting.

Written by the indexing model from the issue text.