Add start time to fixed price minter

[ryley-o]

Idea from @sarahrossien - adding a start time to the next iteration of our fixed price minters would eliminate the need for artists to send a tx to unpause their projects at the start time of a project. This would improve artist experience, and would probably also improve user experience due to a more reliable start time.

This should be relatively simple to implement since we already have a "start time" capability in our automated DA minters.

[jakerockland]

I like it – !vibe

[ryley-o]

@lyaunzbe - this might make sense to implement (as a follow-on PR) in our new set of minters.
Cc @jakerockland

[jakerockland]

@lyaunzbe - this might make sense to implement (as a follow-on PR) in our new set of minters. Cc @jakerockland

+++; @tlip was also interested in this topic, so he may also send us a PR to this effect 👀 💜