feat(sdk): Export stream metadata utils (#2971)

Export `parseStreamMetadata()` and `getStreamPartitionCount()` utility
functions. Note that we've added word _stream_ to make it more explicit
which kind of metadata these process.

The `getStreamPartitionCount()` is needed e.g. when parsing
`StreamMetadata` which has been emitted from `streamCreated` event. For
other usages `parseStreamMetadata()` is maybe useful.

packages/sdk/src/exports.ts

@@ -3,7 +3,7 @@
  */
 export { StreamrClient, SubscribeOptions, ExtraSubscribeOptions } from './StreamrClient'
 export { Stream } from './Stream'
-export { StreamMetadata } from './StreamMetadata'
+export { StreamMetadata, parseMetadata as parseStreamMetadata, getPartitionCount as getStreamPartitionCount } from './StreamMetadata'
 export { Message, MessageMetadata } from './Message'
 export { StreamrClientEvents } from './events'
 export { PublishMetadata } from './publish/Publisher'