The skin style is not refreshed when the color theme is modified

Step to reproduce.

1. Go to the main page, look at the source. The part we are interested in is:

   <link href="      /xwiki/bin/skin/skins/flamingo/style.min.css?cache-version=1617814542000&skin=XWiki.DefaultSkin&#38;colorTheme=xwiki%3AFlamingoThemes.Iceberg
     " rel="stylesheet" type="text/css" media="all" />
   

2. Go the the "Iceberg" theme, make random change, and save the page
3. Go back to the main page, look at the source. The part we are interested in is:

   <link href="      /xwiki/bin/skin/skins/flamingo/style.min.css?cache-version=1617814542000&skin=XWiki.DefaultSkin&#38;colorTheme=xwiki%3AFlamingoThemes.Iceberg
     " rel="stylesheet" type="text/css" media="all" />
   

As you can see, the "cache-version" parameter (that is used to force the browser not to use a cached version of the file when a change is made) has not changed, because it only considers the "style.min.css" file, not the flamingo theme.

As a consequence, the user cannot see the change unless she clears her browser's cache.

To avoid this, we need to add the version of the theme into the query string, so when the theme is changed, the url is different.