Improve gitlab-elasticsearch-indexer logging and traceability

It's currently difficult to determine if the indexer has errors. This is critical when debugging projects are missing data (specifically code) in the index.

Proposal

• documenting how errors generated from the gitlab-elastisearch-indexer can be viewed in GitLab monitoring tools
• determine where logging improvements can be made and create issues to work on the improvements
  • [ ] Convert all logging to JSON format
  • Standardize logger package
  • Change logging output to log/elasticsearch.log