Convert .vm files to markdown and fix remaining rendering warnings

[Bukama]

Improvement proposal

This is a follow up to "MNGSITE-504 - markup warnings" and "MGNSITE-507 - Convert APT to markdown" (after #507 is merged) to get the large and "all-possible-done" JIRA issue closed.

As of today it's not possible to convert .vm files to markdown, because the remaining pages use calculated values (e.g. ${context.get("version.maven-fluido-skin")} in 404.xdoc.vm. As a follow up the remaining rendering warnings in those files can't be fixed.

As of today (2025-01-10) the following warnings are the only ones and they all come from errors/404.xml.vm (see #614 ):

[WARNING] Unrecognized xdoc tag <base> at [31:52]
[WARNING] Unrecognized xdoc tag <link> at [33:100]
[WARNING] Unrecognized xdoc tag <link> at [34:75]
[WARNING] Unrecognized xdoc tag <link> at [35:90]

When it's possible to convert the files, this issue should be the base to do so and fixing the rendering warnings while converting.