Documentation for graceful shutdown

[masaori335]

Drain feature is added by #2962. It looks like there're some way to trigger draining now.

• traffic_ctl drain
• traffic_ctl stop|restart --drain
• Set Connection: close header by header_rewrite plugin (https://docs.trafficserver.apache.org/en/8.0.x/admin-guide/plugins/header_rewrite.en.html#close-connections-for-draining)

It'd be great if we have docs of them and best practice of graceful shutdown.

[maskit]

cc @zizhong

[mlibbey]

Close this out with the merge of #4492?

[maskit]

Unfortunately, no. We also need documentation for traffic_ctls subcommand and options for draining.
https://docs.trafficserver.apache.org/en/8.0.x/appendices/command-line/traffic_ctl.en.html?highlight=traffic_ctl

[masaori335]

Jeremy pointed out another way to trigger graceful shutdown on users list.

If the main purpose here is to issue a 'Connection:close'
why not just disable client facing http keep-alive ?

traffic_ctl config set proxy.config.http.keep_alive_enabled_in 0

[bryancall]

@bneradt Wants to work on this