Feat/meteor integration

[mahyarkarimi]

This pull request adds Meteor.js framework integration for node backend. Due to Meteor.js issue with AsyncLocalStorage from "async_hooks" and its async/await implementation with fibers, this feature adds a run-context based on fibers npm package to support complete integration with the Meteor.js.
In order to set names of the transactions the usePathAsTransactionName must be set to true.

Usage:
import client from 'elastic-apm-node-meteor';
client.start({
serverUrl: '...',
serviceName: '...',
environment: '...',
contextManager: 'fibers',
usePathAsTransactionName: true,
});

Checklist

• Implement code
• Add tests
• Update TypeScript typings
• Update documentation
• Add CHANGELOG.asciidoc entry
• Commit message follows commit guidelines

[trentm]

@mahyarkarimi Thank you for the impressive work that you've done here!

Unfortunately we won't be accepting a change to add Fibers support. My understanding (laverdet/node-fibers#450) is that Fibers is no longer a viable option for async programming in recent Node.js versions. We don't want to add a dependency on and support for the fibers package -- it adds some complexity and maintenance burden to this project that we don't want to take on.