Add test to check if the embedded bot service being used is in the
registry or not.
Add test to check if the bot being added to the registry has a valid
bot corresponding to it.
Move 'get_bot_handler' to 'zerver/lib/bot_lib.py' as it is an independent
function, not related to the 'EmbeddedBotWorker' class that it was
previously a part of.
Splitting bot_lib.py file into 2 files led to unnecessary
redirection of the code workflow. For an embedded bot/service to
send a reply, it was being redirected 3 times.
First, the code flow comes to "EmbeddedBotHandler" class to send
reply, then it goes to the common function in "zulip_bots/lib.py",
then it would come back to "EmbeddedBotHandler". Later on, if we
create an abstract class, from where the bot work flow would
directly hit and then from there it is classified into
EmbeddedBotHandler or ExternalBotHandler and accordingly it would
get redirected.
Now, first the bot flow goes to it's handler class External or
Embedded (where we pass that this is External or Embedded bot as
parameter) and then goes to a common point and then comes back to
the same class.
This is required, since we just reorganized the python-zulip-api
repository into 3 packages.
A nice side effect is that we get to eliminate some now-unnecessary
code for editing sys.path.