Need 'wp_sitemaps_{provider}_url_list' filter for caching.

[jsmoriss]

Currently, there is a wp_sitemaps_posts_pre_url_list filter, which can be used to build a custom URL list or retrieve it from cache, but there is no filter that would allow us to filter the default URL list or save it to cache.

Before returning from get_url_list(), it would be great to have a wp_sitemaps_posts_url_list filter, which would allow us to filter the default URL list or save it to cache.

[swissspidy]

IIRC we did not implement this to avoid prevent devs from using the filter to add additional entries, as it would mess with pagination. Maybe we can add an action hook instead?