header_filter and body_filter handlers are not supported

[vtlkvl]

header_filter and body_filter handlers do not work because they are not supported in https://github.com/Kong/kong-python-pdk/blob/master/kong_pdk/module.py#L31. If it is required to do post-processing of headers, it's only possible with response header, but the thing is that it's going to active buffering automatically which is not really required as long as you just need to update headers. It would be really nice to add support for header_filter and body_filter.

[jschmid1]

Thank you for your valuable input @vtlkvl. I appreciate your contribution and will be sure to discuss your ideas with the team. Your feedback is much appreciated.