Remove usage of Node domains

[AbhiPrasad]

Problem Statement

Domains are deprecated - we should switch off them.

https://nodejs.org/api/domain.html#domain

Solution Brainstorm

Async hooks are avaliable since 8.x, but at Experimental stability.

https://nodejs.org/api/async_hooks.html

When we remove Node 6 support in v7, we can evaluate making the switch

[xr0master]

I think that the main challenge is that, thanks to the domain, a separate scoping is made, where errors are caught and breadcrumbs for this scoping. Sentry creates a scope for the process, but the node.js does not have classical parallelism, and it turns out that the scope becomes global for all incoming requests.

To remove the domain, it needs to reconsider the main concept of ​​Sentry. Create scopes for each request, and at the same time, the scopes should be stored in the hub in parallel, and not stacked on each other. I think, in order not to destroy the existing concept for other languages, it is worth replacing the scope stack with a scope tree. Such the tree store will allow us to create inheritance similar to stacks, but at the same time scopes can be parallel and inherited from the global scope.

[HazAT]

When we work on async_hooks - we probably forget that this issue exists. Closing - but we are going to do it :)