git blame: Display GitHub avatars in blame tooltips, if available (#10767)

Release Notes:

- Added GitHub avatars to tooltips that appear when hovering over a `git
blame` entry (either inline or in the blame gutter).

Demo:



https://github.com/zed-industries/zed/assets/1185253/295c5aee-3a4e-46aa-812d-495439d8840d

crates/editor/src/editor.rs

@@ -13,6 +13,7 @@
 //!
 //! If you're looking to improve Vim mode, you should check out Vim crate that wraps Editor and overrides its behaviour.
 pub mod actions;
+mod blame_entry_tooltip;
 mod blink_manager;
 pub mod display_map;
 mod editor_settings;