Add a stream proposal type

[scottrepreneur]

Is your feature request related to a problem? Please describe.
I'm always frustrated when grantees don't fulfill their promises. It'd be great to leverage streams for additional accountability.

Describe the solution you'd like
Allow a proposal to use treasury funds to create a sablier (or superfluid) stream

Describe alternatives you've considered
Manually building this can work but is trickier