[UI] Broadcast BBN tx will take long, no loading icon shown

[jrwbabylonlab]

Before this modal show up, it will take almost 5-10s.
There is no feedback shown to user as it looks like stuck on the signing modal.
Consider adding loading icon in the signing modal.
Please ping Dan for the design.

To reproduce this, run in local and add a wait when sending out the bbn transaction after signing