Builder add_retry_config requires intermediate variable binding

[davidsow]

Currently the add_retry_config function of OctocrabBuilder is defined with a different function signature than the others, requiring the builder to be bound to an intermediate variable before building to prevent move issues in the borrow checker.

I can't find any public usages of this function on GitHub, so I believe this odd behavior has gone unnoticed since the function was added.

cc @L1ghtman2k (we spoke about this offline)

Example usage: