Proposal: Don't relativize site links

### New feature, improvement proposal

Currently the [m-site-p parameter `relativizeSiteLinks`](https://maven.apache.org/plugins/maven-site-plugin/site-mojo.html#relativizesitelinks) is not set, i.e. image urls like https://github.com/apache/maven-parent/blob/113f357ac5dcd914f4267841a1353fe5a066e64f/src/site/site.xml#L26 are relativized as `../../images/apache-maven-project-light-theme.svg` which only works once deployed on the ASF webserver, but not for local previews.

Although this impacts all generated sites, I would argue that the additional few bytes for the absolute URL doesn't matter.

Start with the m-site-p `relativizeSiteLinks` parameter and the example configuration in src/site/site.xml. Check how generated image links behave in a local preview, then adjust the relevant setting so those links remain absolute; verify that local previews work without breaking deployed site links.

Written by the indexing model from the issue text.