feat: Refresh space OpenGraph image on follows count update

[wa0x6e]

Issue

Current OpenGraph image for space is static, without any variables.
We should display the members count in the image.

Challenge

Members count is dynamic, and may refresh frequently.
The image is cached, and need to be regenerated on follows count update.

Solution

As the webhook service does not fire request for space follows and unfollows events, we need to parse the messages table, and detect those changes directly from the hub.