Make consumer.subscribe accept an array of topics

[benvan]

Feature: consumer.subscribe now accepts String, String[] or RegExp

Motivation: At work, many of our consumers subscribe to a handful of related topics. Reducing the number of consumer.subscribe calls in the proposed manner significantly reduces our consumer startup time (50%)

Justification: Using RegExp is already essentially supplying a string array, just indirectly. If you know the topics you want to subscribe to, this avoids you needing to craft a regex which is built from those topic names (and the cost of the subsequent call to the broker to download the topic list)

Note: This PR does not have an associated issue - if this is a necessary requisite then apologies in advance and I'm happy to oblige

[Nevon]

Makes sense. I would just like to deprecate the topic argument and instead have topics: string[] | RegExp. We should still accept the topic argument for backwards compatibility, but throw an error if both topic and topics are provided. So the type of ConsumerSubscribeTopic becomes { fromBeginning?: boolean } & ({ topic: string | RegExp; } | { topics: string[] | RegExp; }) Feels weird to have an argument called topic that takes an array.

But then the question becomes, should we also accept multiple regular expressions for topics? You can define one regex to match all the desired topics, but maybe it's easier to have multiple regexes. So it'd be { fromBeginning?: boolean } & ({ topic: string | RegExp; } | { topics: string[] | RegExp[]; }) in that case.

[benvan]

Definitely agree re. topics vs topic. I'll submit an update, hopefully this weekend.

Regarding the plural regex/string question - I'll make it take multiple regexes unless you have any objections

EDIT: By which I mean { topics: (string | RegExp)[] }. Example usage would be { topics: ["topic-A", /special-topic-[0-9]+/] }

[Nevon]

Originally I was thinking string[] | RegExp[] because mixed-type arrays always make me feel like I must be doing something wrong, but in this case I agree it makes sense to do (string | RegExp)[]

[Nevon]

I went ahead and updated this with the interface we discussed.

[benvan]

Thank you @Nevon!