Request to Increase Sampling Rate for Firebase Performance Monitoring

## What feature would you like to see?
Describe the feature you would like to add, ideally proposing a specific API.

I would like to see a feature that allows users to increase the sampling rate for specific devices or countries in Firebase Performance Monitoring. This could be done by adding a new API that allows users to specify the devices or countries they want to increase the sampling rate for.

## How would you use it?
Tell us how you'd use this feature in your app.

I would use this feature to monitor the performance of specific devices in specific countries for my app. This is because I want to measure the app performance based on the performance of Android devices. When I filter specific devices, the number of sample data is too small, so it is impossible to obtain sufficient and evenly distributed data.

For example, I would like to compare the performance between countries for the same spec devices for a particular trace, but the values are too different because the samples are too small. With the ability to increase the sampling rate for specific devices or countries, I would be able to obtain more accurate and reliable data about the performance of my app.

I believe that this would be a valuable addition to Firebase Performance Monitoring, and it would allow us to better understand the performance of our app for our users.

The above message has also been uploaded to Firebase Support as Case 10239678, so please check it.