[API] keep tags attached to previous subscribers

[tmtung144]

Sorry my english is not good!

I often have to work through the API and there are a few things that I feel need to be more suitable.
I don't see an api capable of creating new subscribers in bulk using the API (I'm ready to pr)
I proceed to create this API in the job queue, it's ok!
But job-queue can't return new subscriber list immediately so I can use API POST /api/v1/tags/{tagId}/subscribers

I proceed to add subscribers based on your api service but your tags sync default configuration will delete previously attached user tags, so I had to rewrite the service completely new just different configuration as below .

My PR is default false when sync tags but you can enable the option with config.

[JonoB]

The problem with this implementation is that there is now no way to actually remove tags from a subscriber.

[Seb33300]

This feature is now supported in V2 right?
https://sendportal.io/docs/v2/api/tag-subscribers#update

If you want to assign a tag to additional subscribers without removing existing ones, you should use the Store endpoint.

Use the POST endpoint to add new subscribers and PUT endpoint to replace all subscribers?