httr2 1.0.6

• Fix stochastic test failure, particularly on CRAN (#572)
• New oauth_cache_clear() is an exported end point to clear the OAuth cache.
• New req_auth_aws_v4() signs request using AWS's special format (#562, #566).
• req_cache() no longer retrieves anything but GET requests from the cache.
• New resp_stream_aws() to retrieve AWS's special streaming format. With thanks to https://github.com/lifion/lifion-aws-event-stream/ for a simple reference implementation.