Add Gleam icon (#19887)

I took a shot at creating an icon version of the Gleam logo in response
to https://github.com/zed-industries/zed/pull/19529

Release Notes:

- Added an icon for Gleam files.


![image](https://github.com/user-attachments/assets/97432ded-342f-4d87-8eb2-dc9145513d8c)

<img width="231" alt="Screenshot 2024-10-29 at 9 46 33 AM"
src="https://github.com/user-attachments/assets/c957c98f-3da0-4b92-bc21-2a5adca1daa3">

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Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>