refactoring function ngx_http_push_stream_free_message_memory_locked and adding function ngx_http_push_stream_create_str to be easy create an ngx_str_t

refactoring the function ngx_http_push_stream_send_response_all_channels_info_detailed to not response as a chuncked response

fixing bug when apply message and channel name to template with values containing the same template pattern

- creating different timers to clear the memory, one for expired messages and another for empty channels

fix bug on function ngx_http_push_stream_collect_expired_messages_and_empty_channels caused by high concurrency

- add function ngx_http_push_stream_find_channel_locked to search for a channel in a locked memory area
- fix memory allocation for channel id