Detect zlib on configure script

[maskit]

On fresh Ubuntu 18.04 env, I saw this compile error, but the availability of zlib should be checked on configure script.

make[2]: Entering directory '/home/mkitajo/src/trafficserver/src/tscpp/api'
  CXX      libtscppapi_la-AsyncHttpFetch.lo
  CXX      libtscppapi_la-AsyncTimer.lo
  CXX      libtscppapi_la-CaseInsensitiveStringComparator.lo
  CXX      libtscppapi_la-ClientRequest.lo
  CXX      libtscppapi_la-Continuation.lo
  CXX      libtscppapi_la-GlobalPlugin.lo
  CXX      libtscppapi_la-GzipDeflateTransformation.lo
GzipDeflateTransformation.cc:24:10: fatal error: zlib.h: No such file or directory
 #include <zlib.h>
          ^~~~~~~~
compilation terminated.
Makefile:798: recipe for target 'libtscppapi_la-GzipDeflateTransformation.lo' failed

[bryancall]

We do have some checks for zlib:

#
# Check for zlib presence and usability
TS_CHECK_ZLIB