Add GitHub Action for publishing the extension CLI (#9542)

This PR adds a GitHub Action for publishing the extension CLI.

When the `extension-cli` tag is pushed, this Action will run, build the
`zed-extension` binary, and upload it to DigitalOcean for consumption.

This will allow us to consume the pre-built binary in the CI for the
extensions repo.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>

script/upload-extension-cli

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+bash -euo pipefail
+source script/lib/blob-store.sh
+
+commit=$1
+if [ "$#" -ne 1 ] || ! [[ $commit =~ ^[0-9a-f]{40}$ ]]; then
+    echo "Usage: $0 <git-sha>"
+    exit 1
+fi
+
+bucket_name="zed-extension-cli"
+target_triple=$(rustc -vV | sed -n 's|host: ||p')
+
+upload_to_blob_store_public $bucket_name "target/release/zed-extension" "${commit}/${target_triple}/zed-extension"