Changes to Discover Startup Platform Posts

api operation id startup_platform_posts removed and replaced with get_api_v3_discover_startup_platform_posts

the data/items/id response's property format changed from uuid to no format for status 200

for the query request parameter limit, default value was changed from 100 to 30

for the query request parameter post_types, the type of property items/ changed from no type to string

added the non-success response with the status 503