API for setting app launch span sample rate #5047
Description
Problem Statement
Users can set a global sample rate, or use a custom sampler, but there isn't a clear way to set a sample rate for app launches. Many apps will have hundreds of spans throughout the lifetime of a process but only one app launch. A reasonable global sample rate might greatly reduce the number of app launch spans that get sent to Sentry even though they are arguably the most important spans. We should provide an easy way to customize the sample rate just for app launch spans.
Solution Brainstorm
One options would be to have an API to identify the span/transaction as being for app launch in the custom sampler, so you wouldn't set a global sample rate but you'd check if the span was app launch and return a different sample rate than a default value.