A custom AlertNode for writing annotations into Chronograf

This alertNode would allow users to easily write annotations into chronograf using the api calls. A user would be able to configure the following options:
- a template to be used for the name
- a chronograf base url
- oauth credentials
- an option to annotation twice (on the way up and on the way down), or use a timespan, which would add an initial annotation, then update it once the issue is resolved to be a range.

Start by locating existing alertNode implementations and the code that performs external API calls. Read how nodes handle configuration, OAuth credentials, templates, and lifecycle updates before defining the Chronograf integration. Done means users can configure the requested options and create either separate annotations or an annotation range through Chronograf.

Written by the indexing model from the issue text.