chore(autofix): Add some metrics for explorer autofix triggers

[Zylphrex]

Emit some metrics for when explorer autofix is triggered along with referrers so we know what triggered it.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[github-actions]

Backend Test Failures

Failures on e5cd6ac in this run:

tests/sentry/seer/autofix/test_autofix_on_completion_hook.py::TestAutofixOnCompletionHookPipeline::test_maybe_continue_pipeline_pushes_changes_for_open_pr — log

tests/sentry/seer/autofix/test_autofix_on_completion_hook.py:261: in test_maybe_continue_pipeline_pushes_changes_for_open_pr
    mock_push_changes.assert_called_once_with(self.group, 123, state=state)
/opt/hostedtoolcache/Python/3.13.1/x64/lib/python3.13/unittest/mock.py:989: in assert_called_once_with
    return self.assert_called_with(*args, **kwargs)
/opt/hostedtoolcache/Python/3.13.1/x64/lib/python3.13/unittest/mock.py:977: in assert_called_with
    raise AssertionError(_error_message()) from cause
E   AssertionError: expected call not found.
E   Expected: trigger_push_changes(<Group at 0x7f078efb39d0: id=213, project_id=4557866002481152>, 123, state=SeerRunState(run_id=123, blocks=[MemoryBlock(id='block-root-cause', message=Message(role='assistant', content='message root cause', tool_calls=None, metadata={'step': 'root_cause'}), timestamp='2026-02-10T00:00:00Z', loading=False, artifacts=[Artifact(key='root_cause', data={'one_line_description': 'Null pointer in auth module'}, reason='explorer')], file_patches=None, merged_file_patches=None, pr_commit_shas=None), MemoryBlock(id='block-solution', message=Message(role='assistant', content='message solution', tool_calls=None, metadata={'step': 'solution'}), timestamp='2026-02-10T00:00:00Z', loading=False, artifacts=[Artifact(key='solution', data={}, reason='explorer')], file_patches=None, merged_file_patches=None, pr_commit_shas=None), MemoryBlock(id='block-code-changes', message=Message(role='assistant', content='message code changes', tool_calls=None, metadata={'step': 'code_changes'}), timestamp='2026-02-10T00:00:00Z', loading=False, artifacts=[], file_patches=None, merged_file_patches=[ExplorerFilePatch(repo_name='test-repo', patch=FilePatch(path='test.py', type='M', added=5, removed=2), diff='')], pr_commit_shas=None)], status='completed', updated_at='2026-02-10T00:00:00Z', pending_user_input=None, repo_pr_states={}, metadata={'group_id': 213, 'stopping_point': 'open_pr'}, coding_agents={}))
E     Actual: trigger_push_changes(<Group at 0x7f078efb3390: id=213, project_id=4557866002481152>, 123, referrer=<AutofixReferrer.GROUP_AUTOFIX_ENDPOINT: 'api.group_ai_autofix'>, state=SeerRunState(run_id=123, blocks=[MemoryBlock(id='block-root-cause', message=Message(role='assistant', content='message root cause', tool_calls=None, metadata={'step': 'root_cause'}), timestamp='2026-02-10T00:00:00Z', loading=False, artifacts=[Artifact(key='root_cause', data={'one_line_description': 'Null pointer in auth module'}, reason='explorer')], file_patches=None, merged_file_patches=None, pr_commit_shas=None), MemoryBlock(id='block-solution', message=Message(role='assistant', content='message solution', tool_calls=None, metadata={'step': 'solution'}), timestamp='2026-02-10T00:00:00Z', loading=False, artifacts=[Artifact(key='solution', data={}, reason='explorer')], file_patches=None, merged_file_patches=None, pr_commit_shas=None), MemoryBlock(id='block-code-changes', message=Message(role='assistant', content='message code changes', tool_calls=None, metadata={'step': 'code_changes'}), timestamp='2026-02-10T00:00:00Z', loading=False, artifacts=[], file_patches=None, merged_file_patches=[ExplorerFilePatch(repo_name='test-repo', patch=FilePatch(path='test.py', type='M', added=5, removed=2), diff='')], pr_commit_shas=None)], status='completed', updated_at='2026-02-10T00:00:00Z', pending_user_input=None, repo_pr_states={}, metadata={'group_id': 213, 'stopping_point': 'open_pr'}, coding_agents={}))