chore(nodejs): expose SenderOptions class

[nicochatzi]

Expose the SenderOptions class for consumers to be able to build options from a configuration string. Useful for using SenderBuffer and SenderTransport without going through the Sender.

Context:

We would like to use the SenderTransport, SenderBuffer and SenderOptions classes for a custom Sender that caches the buffer contents. However, SenderOptions is only exposed as a type and therefore we cannot use SenderOptions.fromConfig and other methods.

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