add configuration plugin

[cynthiagu23]

add 3 configurations for the environment:

1. --sleep-in-sec to allow enough sleep time for async log to write out
2. --keep-tmp to keep the /tmp folder for debug purpose
3. --standalone-ats-port allow a separate deployment of ats

[jacksontj]

This will probably need to follow the same server_ports markup that we have in records.config-- since ATS ports have different attributes associated with them (such as ipv4:443 -- https://docs.trafficserver.apache.org/en/latest/reference/configuration/records.config.en.html#proxy-config-http-server-ports)

[jacksontj]

Are both if checks necessary? And if so, can we put them in one line?

[jacksontj]

@cynthiagu23 Few comments left unfixed, once those are taken care of I think we are good to merge :)

[jacksontj]

is ZPL compatible with Apache?

[igalic]

i think all we have to do, is add this notice to the NOTICE file, like we do in ats itself
https://github.com/apache/trafficserver/blob/master/NOTICE