Add Retention Priorities

[DarkByteZero]

Problem Statement

Add Feature of Sentry Saas to Selfhosted: https://docs.sentry.io/product/performance/retention-priorities/

This would add a new core concept of Sentry eg. Dynamic Sampling to Self-Hosted.

Solution Brainstorm

Most of the Dynamic Sampling is handled by Relay and Tasks running in celery.

I found the following Feature Flags to enable the UI:

"organizations:dynamic-sampling", "organizations:investigation-bias"

But i think the tasks needed, currently don't run on self-hosted, and there is a variable set on the org that needs to be true.