[Dev] enable opensearch snapshot for Darwin

Enable the downloading of Darwin for running the command
`yarn opensearch snapshot`.

Darwin is not officially supported but snapshots are being
built here:
https://build.ci.opensearch.org/job/distribution-build-opensearch/

Issue resolved:
#2944

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>

packages/osd-opensearch/src/artifact.js

@@ -188,8 +188,8 @@ async function getArtifactSpecForSnapshotFromUrl(urlVersion, log) {
   const arch = process.arch === 'arm64' ? 'arm64' : 'x64';
   const extension = process.platform === 'win32' ? 'zip' : 'tar.gz';
 
-  if (platform !== 'linux' && platform !== 'windows') {
-    throw createCliError(`Snapshots are only available for Linux and Windows`);
+  if (platform !== 'linux' && platform !== 'windows' && platform !== 'darwin') {
+    throw createCliError(`Snapshots are only available for Linux, Windows, and Darwin`);
   }
 
   const latestUrl = `${DAILY_SNAPSHOTS_BASE_URL}/${desiredVersion}-SNAPSHOT`;

packages/osd-opensearch/src/artifact.test.js

@@ -163,10 +163,10 @@ describe('Artifact', () => {
         });
       });
 
-      it('should throw when on a non-Linux or non-Windows platform', async () => {
+      it('should throw when on a non-Linux, non-Windows, non-Darwin platform', async () => {
         Object.defineProperties(process, {
           platform: {
-            value: 'darwin',
+            value: 'android',
           },
           arch: {
             value: ORIGINAL_ARCHITECTURE,