zulip-cli: Replace harcoded zuliprc path with the one used in zulip_bots/run.py

[rht]

Originally posted by @andersk in #663 (comment)

This is the PR for zulip-cli: #663.
We want to replace the hardcoded zuliprc path (currently ~/zuliprc) to use something along the line of

python-zulip-api/zulip_bots/zulip_bots/run.py

Line 55 in 717a549

def exit_gracefully_if_zulip_config_is_missing(config_file: Optional[str]) -> None:

. The mechanism in run.py needs to be abstracted out and provided by the core library.