- add keyring for gpg validation
- spec file cleanups

For example, if GOAWAY frame has been received, a
* https://nghttp2.org/blog/2023/05/10/nghttp2-v1-53-0/
checking leading and trailing white spaces against HTTP field value.
* https://nghttp2.org/blog/2022/08/22/nghttp2-v1-49-0/
* third-party: Bump neverbleed based on the latest head (GH-1708)
* see https://nghttp2.org/blog/2022/02/23/nghttp2-v1-47-0/
* see https://nghttp2.org/blog/2021/10/19/nghttp2-v1-46-0/
* nghttpx: Fix logging integer
- Conditionally remove dependecy on jemalloc for SLE-12
if table size is changed from default
* Add nghttp2_option_set_max_send_header_block_length API
* Fix warning: declaration of 'free' shadows a global declaration
* nghttpx: Add healthmon parameter to -f option to enable health
* nghttpx: Add --api-max-request-body option to set maximum API
* nghttpx: Add api parameter to --frontend option to mark API
* h2load: Add content-length header field for HTTP/2 and SPDY as
* Run error callback when peer does not send initial SETTINGS
* nghttpx: Fix bug that server push from mruby script did not
* nghttpx: Try next HTTP/1 backend address when connection
* nghttpx: Retry next HTTP/2 backend address when connection
* nghttpx: Enable link header field based push for non-final
* nghttpx: Fix bug that logger wrote string which was not
* nghttpx: Fix bug that backend tls keyword did not work with -s
* lib: Add nghttp2_error_callback to tell application human
* lib: Add nghttp2_http2_strerror() to return HTTP/2 error code
* integration: Disable tests that sometimes break randomly on
* h2load: Fix bug that initial max concurrent streams was too