Implement data retention in storage layer

[petethepig]

Feature Description

Sometimes it doesn't make sense to store data indefinitely so we need to implement a way to do data retention.

Internally Pyroscope uses segment trees to store the data.
See our Storage Design Doc for more context.

We need to add a new retention threshold parameter that would control how much data (in days) can be stored in pyroscope. Then we would run some sort of a Cleanup method every once in a while to delete old data:

TODO

• Implement a method that would delete data before a certain time on segment tree and return a list of trees that need also need to be deleted.
• cover it with specs
• add a retention option to config
• in storage package, put conditions in Put method that would prevent data ingestions past the retention threshold
• in storage package add a method that would delete segment tree nodes as well as relevant trees
• create a separate goroutine that would call this cleanup method every X minutes