Feature Request: Blob Binding (out): Set Metadata Properties Like CacheControl and ContentType

It would be handy to be able to set metadata properties for Blobs like Cache-Control and Content-Type.

#### Known workarounds

It is required to use the SDK for creating blobs that require custom metadata property values.

#### Related information

Perhaps a "propeties" value could be added to the json for out blob.

To Set the Value Statically with Functions.json

```json
{
"name": "outputBlob",
"type": "blob",
"direction": "out",
"path": "{container}/{blob}",
"connection": "AZURE_STORAGE_CONNECTION_STRING",
"properties": {
"cacheControl": "public, max-age 86400",
"contentType": "application/json",
"contentEncoding": "gzip"
}
}
```

To Set the Value at Runtime:

```javascript

context.bindings.outputBlob = {data: '...'};
context.bindingsMetadata.outputBlob.properties = {contentType:'application/json'};

```

No source files or tests are named. Start by tracing the Blob output binding and how its JSON configuration and runtime metadata are handled; done should mean Cache-Control, Content-Type, Content-Encoding, and similar properties can be supplied statically or at runtime and applied to created blobs.

Written by the indexing model from the issue text.