break down messages due to slack msg limit

Slack API has a limit on message length, and adding bm3dornl happens to exceed that limit. This MR breaks down the messages and sending them one category at a time.

app.py

@@ -251,9 +251,15 @@ app = App(token=os.environ["SLACK_BOT_TOKEN"], name="Amaterasu")
 def greetings(ack, say):
     ack()
     say("Build status summary for Neutron projects:")
-    status_blocks = {"blocks": get_status_blocks()}
-    say(status_blocks)
 
+    # NOTE: Slack API has a limit of 50 blocks per message, so we need to break it down
+    # into smaller messages
+    # 0. Legend
+    say({"blocks": legend()})
+    # 1. Gitlab projects
+    say({"blocks": gitlab_status_blocks()})
+    # 2. Github projects
+    say({"blocks": github_status_blocks() + mantid_block()})
 
 # Start your app
 if __name__ == "__main__":