Add `BlobClientDownloadResultHeaders::content_type()`

[tjallingt]

Feature Summary

BlobClientDownloadResultHeaders::content_type()

Feature Description

BlockBlobClientUploadOptions contains a blob_content_type: Option<String> which states

Optional. Sets the blob’s content type. If specified, this property is stored with the blob and returned with a read request.

But since it is missing from the BlobClientDownloadResultHeaders trait (and its siblings) it is tricky to access.

Use Case

Reading the content type of a blob retrieved from BlobClient::download()

Alternatives

No response

Additional Context

No response

[tjallingt]

This seems to be caused by the typespec from https://github.com/Azure/azure-rest-api-specs

This appears to be the definition of the header name and value:
https://github.com/Azure/azure-rest-api-specs/blob/05d1c25a769ec0cbf9ea44dac56b9e795eea92d7/specification/storage/Microsoft.BlobStorage/models.tsp#L1906-L1911

This seems to be included in op setProperties and op upload (for example).
But it is missing from op download and op getProperties:

https://github.com/Azure/azure-rest-api-specs/blob/05d1c25a769ec0cbf9ea44dac56b9e795eea92d7/specification/storage/Microsoft.BlobStorage/routes.tsp#L705-L838

Edit also reported here Azure/azure-rest-api-specs#40801