Uploading blob metadata with invalid key should fail

### Which service(blob, file, queue, table) does this issue concern?
Blob
### Which version of the Azurite was used?
3.4.0
### Where do you get Azurite? (npm, DockerHub, NuGet, Visual Studio Code Extension)
npm
### What's the Node.js version?
v11.10.0
### What problem was encountered?
When I try to add metadata to a blob where the key is something that is not valid (e.g. the string "1"), I expect the upload of the metadata to fail. It does not when using Azurite, but the old Azure Storage Emulator had the correct behavior.
### Steps to reproduce the issue?
Create blob. Set the metadata as key:"1", value:"value". Upload metadata. Expect that the call fails, but it seems to succeed.
### Have you found a mitigation/solution?
Disabling the test we have in our code for now.