fix(seer): Handle enum deserialization in autofix tasks

[sentry]

This PR addresses the NoRetriesRemainingError occurring in sentry.tasks.autofix.trigger_autofix_from_issue_summary, which was caused by an AttributeError: 'str' object has no attribute 'value'.

Problem:
When AutofixStoppingPoint and AutofixReferrer enum instances are passed as parameters to the _trigger_autofix_task Celery task, the Celery serialization process converts these enums into their string representations (e.g., 'root_cause'). Upon deserialization, the task receives these parameters as plain strings, not as StrEnum objects. Downstream functions, such as trigger_autofix_explorer, then attempt to access the .value attribute on these string objects, leading to an AttributeError.

Solution:

1. Updated _trigger_autofix_task signature: Modified the type annotations for stopping_point and referrer parameters in src/sentry/seer/autofix/issue_summary.py to AutofixStoppingPoint | str | None and AutofixReferrer | str respectively. This clarifies that the task can receive these parameters as either enum instances or their string values after deserialization.
2. Enum Reconstruction: Added logic at the beginning of the _trigger_autofix_task function to explicitly convert stopping_point and referrer back into their respective StrEnum types if they are received as strings. This ensures that by the time these parameters are used by downstream functions, they are always proper enum instances.

This fix ensures that the task correctly handles the deserialization of enum parameters, preventing the AttributeError and the subsequent task retry exhaustion.

Fixes SENTRY-5AYM

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

[Mihir-Mavalankar]

Not sure why this only affects automations you org though.