Send up Zed version with edit prediction and completion requests (#30136)

This PR makes it so we send up an `x-zed-version` header with the
client's version when making a request to llm.zed.dev for edit
predictions and completions.

Release Notes:

- N/A

crates/language_models/Cargo.toml

@@ -41,6 +41,7 @@ open_ai = { workspace = true, features = ["schemars"] }
 partial-json-fixer.workspace = true
 project.workspace = true
 proto.workspace = true
+release_channel.workspace = true
 schemars.workspace = true
 serde.workspace = true
 serde_json.workspace = true