Add an implementation of GitHostingProvider for repositories hosted on
https://chromium.googlesource.com. Pull requests target the Gerrit
instance at https://chromium-review.googlesource.com and avatar images
are fetched using the Gerrit REST API.

<img width="513" alt="Screenshot 2025-02-20 at 6 43 37 PM"
src="https://github.com/user-attachments/assets/867af988-594d-45ea-8482-e40517443c73"
/>

<img width="511" alt="Screenshot 2025-02-20 at 6 43 51 PM"
src="https://github.com/user-attachments/assets/1d412904-048d-4a2d-8494-0837e75f8d61"
/>

Release Notes:

- Added support for repositories hosted on `chromium.googlesource.com`
for Git blames and permalinks.

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Co-authored-by: Marshall Bowers <git@maxdeviant.com>