Add `created_by_user_avatar_url` parameter support in `async_create_issue_advanced

[hco]

Missing created_by_user_avatar_url parameter support in async_create_issue_advanced. The async_create_issue method (line 328) supports both created_by_user and created_by_user_avatar_url parameters, but async_create_issue_advanced only supports created_by_user (line 434) without the avatar URL parameter. This creates an inconsistency in the API.

Consider adding the created_by_user_avatar_url parameter to async_create_issue_advanced to maintain feature parity between both methods.

Originally posted by @Copilot in #3 (comment)