feat(docuploader): add destination-prefix option (#26)

The prefix option will be used when uploading DocFX YAML. We need to
distinguish HTML docs vs DocFX YAML. Then, another job will convert the
YAML to HTML. This way, all DocFX tarballs can start with docfx- and we can
strip that prefix when uploading the resulting HTML.

docuploader/__main__.py

@@ -55,11 +55,17 @@ def main():
     help="Path to the credentials file to use for Google Cloud Storage.",
 )
 @click.option("--metadata-file", default=None, help="Path to the docs.metadata file.")
+@click.option(
+    "--destination-prefix",
+    default=None,
+    help="Prefix to include when uploading tar file. A - will be added after the prefix, if there is one.",
+)
 @click.argument("documentation_path")
 def upload(
     staging_bucket: str,
     credentials: str,
     metadata_file: Optional[str],
+    destination_prefix: str,
     documentation_path: str,
 ):
     if not credentials:
@@ -112,11 +118,13 @@ def upload(
         fh.close()
         tar_filename = fh.name
         docuploader.tar.compress(documentation_path, tar_filename)
-        docuploader.log.success(f"Cool, I have those tarred up.")
-        docuploader.log.info(f"Okay, I'm sending them to the cloud™ now.")
+        docuploader.log.success("Cool, I have those tarred up.")
+        docuploader.log.info("Okay, I'm sending them to the cloud™ now.")
         destination_name = (
             f"{metadata.language}-{metadata.name}-{metadata.version}.tar.gz"
         )
+        if destination_prefix:
+            destination_name = f"{destination_prefix}-{destination_name}"
 
         docuploader.upload.upload(
             source=tar_filename,