Add sync update route to API

[ryanwjackson]

Is your feature request related to a problem? Please describe.
If a sync is incorrect, it cannot be updated.

Describe the solution you'd like
Add a PUT /syncs/:id API route for updating syncs.

Describe alternatives you've considered

• Though probably more correct, you could skip all remaining queued/blocked syncs and re-queue them as new ones.

Additional context
Leftover from #16

[mattgmarcus]

This is a good ticket to do too.