Add the option to disable the output of lastmod, changefreq and priority in sitemaps

Are you working on that feature? If yes feel free to reassign it to yourself and provide a merge request so people can use it to patch the module. This won't be going into the main branch however as
a) file size should not be a concern as we split the sitemaps into smaller sitemaps if they are too big
b) this can easily be achieved by creating a custom sitemap generator plugin and configuring the sitemap to use it instead of the default plugin. Implementation is as easy as extending DefaultSitemapGeneratorPlugin and overriding its ::addUrl() function.

I manually applied the changes in the merge and seems to be working just fine with 4.1.6 . I believe this could be inside the module since google does not care anymore about these metrics.

If not could someone provide a patch?