* Add `--ping` as a CLI option

This builds in the functionality asked for in #1470; it allows pgcli to
replace `pg_isready` from the postgresql command line toolchain

* Update the changelog and AUTHORS

* Use click.echo

pgcli.echo doesn't seem to actually _echo_ anything

* Add integ tests for the ping feature

* Refactor try / else

Co-authored-by: Damien Baty <damien@damienbaty.com>

* Unused variable

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Co-authored-by: Irina Truong <637013+j-bennet@users.noreply.github.com>
Co-authored-by: Damien Baty <damien@damienbaty.com>