zulip_bots: Generate static files during provisioning.

This commit implements support for copying over static files
for all bots in the zulip_bots package to
static/generated/bots/ during provisioning. This directory
isn't tracked by Git. This allows us to have access to files
stored in an arbitrary zulip_bots package directory somewhere
on the system. For now, logo.* and doc.md files are copied over.

This commit should act as a starting point for extending our
macro-based Markdown framework to our bots/API packages'
documentation and eventually rendering these static files
alongside our webhooks' documentation.

tools/lib/provision.py

@@ -277,6 +277,9 @@ def main(options):
     run(["sudo", "chown", "%s:%s" % (user_id, user_id), EMOJI_CACHE_PATH])
     run(["tools/setup/emoji/build_emoji"])
 
+    # copy over static files from the zulip_bots package
+    run(["tools/setup/generate_zulip_bots_static_files"])
+
     run(["tools/setup/build_pygments_data.py"])
     run(["scripts/setup/generate_secrets.py", "--development"])
     run(["tools/update-authors-json", "--use-fixture"])