https://demo.toolpad.io/ data fetching feels limited

Related to #592

I was hoping I could rebuild most of the mini-apps that I had created on the staging environment https://master--toolpad.mui.com/ in the demo environment: https://demo.toolpad.io/ but it’s not the case. This makes me wonder:

1. Why not have the default fetch query? Right now, when I click on adding a new query, the select is empty.

1. Why not have a fetch function? If we are worried about the amplification network power that Toolpad can provide to bad actors, then we could limit the number of fetch calls that can be made inside the function. I think that we would also need to limit the number of queries that can be added to the page, because why close one door (fetch) when the other is open (multi queries)?

1. Why not have PostgreSQL? If there is a good reason for it, I think that we should allow people to pick it and then explain why it’s not available. Currently, it feels like the feature doesn’t exist.

1. Why not have Google Sheet? Same to 3.

[prakhargupta1]

Regarding the UX improvements. I would suggest that we do these changes:

1. In the connections drop-down, just like we show in staging env, we should show:

• Function
• fetch
• Postgres (disabled)
• Google Sheets (disabled) For disabled ones we show a message that they are currently available in the self-host version only.

1. Add query should not be a blank list. Like we show in the staging environment, we should show:

• default fetch
• default function
• Movies API
• Covid API
• dog API

1. Self-host button on top.
2. When creating the app, show the message that ‘In case you need to revisit the app later please save the app URL’

[prakhargupta1]

Ok. Let’s then add the message in the footer. That should be fine.