feat: allow bulk subscription with different pubsub topics at the same time

[adklempner]

Description

NextFilter allows to subscribe with an array of decoders but has constrain of them having same pubsub topic.

Current behavior:

• API accepts IDecoder<T> | IDecoder<T>[]
• Throws runtime error: "Cannot subscribe to more than one pubsub topic at the same time"

User Story

As a developer using the Filter API, I want to subscribe with an array of decoders with different pubsub topics.

Proposed Solution / Feature Design

Should be straightforward from the description.

[weboko]

thanks for creating the issue!
I updated the description to make it more realistic

[weboko]

On PM we agreed to remove IDecoder<T>[] and allow to use only one IDecoder<T> for subscribing / querying.
It will affect Store / Filter / LightPush / Relay API.

Any feedback on that @fryorcraken @vpavlin ?

[fryorcraken]

Would be good to understand what the users do. Ultimately, we want to encourage developer to use less content topics at first, but we need to be open to scale up.

It seems to me fine to do this change, and then ready to revert the change at a later stage when we get the demand for it.

[weboko]

Estimated to effort/days: should be straightforward as to replace usage of array to one element.