feat: add switcher new api : check_topic_exist and close_topic

change(feat, refactor):

implementing switcher server : add gflags and handle exception"

fix some tiny bug

implementing switcher and switcher_client

refactor serialize and deserialize concept

refactor switcher

implementing switcher component

refactor SocketSource.Read; add switcher design doc

refactor uint32_t's [de]seri : consider endian

add new tool pipeline draw.py

update socket source and sink's hosted_mode

implementing socket sink and source

add new awaiter SocketAcceptAwaiter and fix some bug in test

refactor: channel_sink and channel_source's hosted_mode method