custom metadata is not stored when a new object is uploaded

[CNDW]

Describe the bug
New objects being created via the google.cloud.storage.Blob api that have had metadata set on the object via blob.metadata are not having the metadata persisted in the emulator.

To Reproduce
The following code snippet will fail when run against the emulator but work when run against GCS

from google.cloud.storage import Client
from tempfile import NamedTemporaryFile

client = Client()
bucket = client.create_bucket("testbucket")
blob = bucket.blob("test.txt")
blob.metadata = {"foo": "bar"}

with NamedTemporaryFile() as file:
    file.write("file-content")
    file.flush()
    file.seek(0)
    blob.upload_from_file(file)
    
uploaded_blob = bucket.get_blob("test.txt")
assert uploaded_blob.metadata == {"foo": "bar"}

Expected behavior
Any attached metadata should persist on the file saved in the emulator

System (please complete the following information):

• OS version: latest gcp-storage-emulator docker image
• Python version: 3.12
• gcp-storage-emulator version: v2024.08.03

Additional context
I have a proposed fix in the following PR
#287