This is multi-stage build which first builds tsearch-extras with the
current version of postgres and then configs postgres for zulip. The
zulip config installs the hunspell dictionaries, stop words file,
tsearch-extras, and creates the initial database.
**Testing Plan:**
1) `docker-compose up` the existing config.
2) Build the new image
3) Edit docker-compose.yml to use the new image id
4) `docker-compose up` and verify full text search is still working.
Jason Michalski