Allow multiple topics to call the same endpoint (#763)
* Allow multiple topics to call the same endpoint
Using the WithTopic builder pattern allows you to specify multiple
topics that route to a single endpoint. Given the topics are unique,
this should be a valid case.
This change allows for a single endpoint to bind to multiple topics.
Note that this can only be done via the EndpointBuilder and not the
TopicAttribute.
https://github.com/dapr/dotnet-sdk/issues/715
* Let TopicAttribute to be specified multiple times
The endpoint builder allowed for multiple WithTopic calls so the
attribute should match that behavior.
