[ticket/12927] core.mcp_queue_get_posts2_query_before

Adding the core.mcp_queue_get_posts2_query_before
event to mcp backend.

PHPBB3-12927
Merge pull request #2824 from brunoais/ticket/12927

[ticket/12927] core.mcp_queue_get_posts2_query_before

* brunoais/ticket/12927:
  [ticket/12927] core.mcp_queue_get_posts2_query_before
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12927] core.mcp_queue_get_posts2_query_before