Feature/elastic 7

[racevedoo]

Description

This PR contains 3 major changes:

• Moves project dependency management from dep to go modules, as v7 of https://github.com/olivere/elastic recommends.
• Upgrades https://github.com/olivere/elastic to v7 for better elasticsearch 7.0 support
• Removes kafka topic name as type from elasticsearch indexing, in favor of _doc. For details, refer to https://www.elastic.co/guide/en/elasticsearch/reference/7.0/removal-of-types.html

Why is this PR needed?

We need to support elasticsearch 7.0

Checklist

• Branch is named acoording to standards (feature/*, fix/*, hotfix/*)
• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Bump project version, if this adds a new feature
• Extended the README / documentation, if necessary

[gppeixoto]

lgtm