Adding setting for custom OpenAI base url

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.11%. Comparing base (8fbaf01) to head (f694e4c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #785 +/- ## ========================================== + Coverage 84.06% 84.11% +0.04% ========================================== Files 83 83 Lines 4011 4023 +12 ========================================== + Hits 3372 3384 +12 Misses 639 639 ``` | [Flag](https://app.codecov.io/gh/chidiwilliams/buzz/pull/785/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | Coverage Δ | | |---|---|---| | [Linux](https://app.codecov.io/gh/chidiwilliams/buzz/pull/785/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `82.27% <100.00%> (+0.05%)` | :arrow_up: | | [macOS](https://app.codecov.io/gh/chidiwilliams/buzz/pull/785/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `82.35% <100.00%> (+0.05%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams#carryforward-flags-in-the-pull-request-comment) to find out more.

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