[1.1.237] Support DW Openpose preprocessor

[huchenlei]

See initial issue here: #1855
Previous release note: #1863
This release does not introduce extra dependencies. The detection model runs on CPU with a reasonable speed.

DW Openpose preprocessor greatly improves the accuracy of openpose detection especially on hands. Here is a comparison used in our unittest:

Input Image:

Openpose Full (Mis-identified finger/ Missing hand):

DW Pose:

With this pose detection accuracy improvements, we are hyped to start re-train the ControlNet openpose model with more accurate annotations. There is a proposal in DW Pose repository: IDEA-Research/DWPose#2.