Restrict one chatbot per messenger page

[bjafri5]

In this issue, we will add a restriction of only one chatbot per messenger page. Currently both a manual chatbot and shopify chatbot can coexist which can cause replies from both chatbots to occur simultaneously.

There are two subtasks to this issue:

• If a user tries to enable a manual chatbot and a shopify chatbot already exists, it will prompt the user that the shopify chatbot will be disabled and by clicking on confirm, the shopify chatbot will be disabled.
• If a user tries to enable a shopify chatbot and a manual chatbot already exists, it will prompt the user that the manual chatbot will be disabled and by clicking on confirm, the manual chatbot will be disabled.

[bjafri5]

@sojharo please test on staging and production

[sojharo]

This is working fine on production and staging.