Increase the event retention period to >90d

### Problem Statement

We want to retain events for more than 90 days, to at least 6 months and ideally more than 1 year.
This will make it easier to debug issues that happen periodically, especially in poducts with yearly releases.
As a way to mitigate the costs, the user could have the option to provide storage for the older events.

### Solution Brainstorm

_No response_

### Product Area

Unknown

No files, tests, or entry points are named. Start by locating how Sentry configures event retention and stores older events, then clarify the product area and requirements for six-month, one-year, and user-provided storage options. Done requires an agreed design and implementation scope, including the cost and retention behavior.

Written by the indexing model from the issue text.