Pattern stops: Inherit unspecified continuous pickup/dropoff attributes from route.

[binh-dam-ibigroup]

After looking into this, the only thing with providing an optional dropdown option is that a user may be confused if they intentionally left the value of continuous_pickup blank to indicate "No continuous stopping pickup." but on the front end we display "(optional)". Given this fact, maybe it's best to interpret a blank value as the default in both the pickup/dropoff type and continuous_pickup/dropoff contexts (i.e. keep the changes as is). Thoughts @binh-dam-ibigroup ?

Another (probably important) thing to consider is the spec allows the stop times with unspecified continuous pickup/drop off to "inherit" those the corresponding settings of the parent route (see spec link above).

Originally posted by @binh-dam-ibigroup in #765 (comment)