Support for filtering logs via before_send_log

[solnic]

I'll update changelog for the entire feature when preparing changelog for 12.0.0.

#skip-changelog

Closes #909

[sentry]

Bug: An unhandled exception in a before_send_log callback will crash the background task, causing the entire batch of logs to be silently lost.
_{Severity: HIGH}

Suggested Fix

Wrap the execution of the user-provided callback within a try/rescue block inside the call_before_send_log function. If an exception is caught, it should be logged appropriately without crashing the task, allowing the remaining logs in the batch to be processed and sent.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: lib/sentry/client.ex#L183-L189

Potential issue: The `before_send_log` callback is executed within a background task
spawned by `Task.Supervisor.start_child()`. The function `call_before_send_log` does not
include any exception handling, such as a `try/rescue` block. If a user-provided
callback raises an exception, it will cause this background task to crash. Because the
task crashes before the logs are sent via an HTTP request, the entire batch of logs
being processed will be silently lost. The application will not be notified of the
failure, and the error will only be visible in Elixir's task error logs, making it a
difficult issue to debug in production.

_{Did we get this right? 👍 / 👎 to inform future reviews.}