feat: aggregate exception events for overrides

[daibhin]

Problem

We are migrating to using the overrides table for fingerprint merging

Changes

Implementing the overrides pattern described in https://github.com/PostHog/product-internal/blob/main/requests-for-comments/2024-10-08-error-tracking-issue-overrides.md#fetching-events

Based on the changes made in #21059 to support lazy table joins

Does this work well for both Cloud and self-hosted?

Yes

How did you test this code?

Added tests back

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ UnboundLocalError: cannot access local variable 'span' where it is not associated with a value posthog.tasks.tasks.process_query_task View Issue
• ‼️ UnboundLocalError: cannot access local variable 'span' where it is not associated with a value posthog.tasks.tasks.process_query_task View Issue

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