Support publishing Grafana annotations when Imbi opslog entries are created/modified

[ryangsteele]

It would be handy if Imbi could create Grafana annotations when an opslog entry is created or updated. There are a few things we'd have to work out, including but not limited to:

• How do we determine the Grafana annotations API URL? Could we derive this from the project's Grafana dashboard URL, if one is defined?
• How to manage authorization tokens required to publish to Grafana's annotations endpoint
• Annotation tags: should there be a default set of tags (e.g., ["imbi-opslog", "$TEAMSLUG", "$PROJECTSLUG", "$ENVIRONMENT"])? Should the list of tags be configurable?