Add Gleam icon (#19887)

I took a shot at creating an icon version of the Gleam logo in response
to #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">

---------

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

assets/icons/file_icons/file_types.json

@@ -58,6 +58,7 @@
     "gitignore": "vcs",
     "gitkeep": "vcs",
     "gitmodules": "vcs",
+    "gleam": "gleam",
     "go": "go",
     "gql": "graphql",
     "graphql": "graphql",
@@ -264,6 +265,9 @@
     "fsharp": {
       "icon": "icons/file_icons/fsharp.svg"
     },
+    "gleam": {
+      "icon": "icons/file_icons/gleam.svg"
+    },
     "go": {
       "icon": "icons/file_icons/go.svg"
     },