Rename index patterns to improve the readability of the data

Sooner than later we should stop and rethink the naming conventions of the indexes patterns being shown in the dashboard. It is really hard to understand for the users. Some examples:
- `github_issues` index pattern stores documents both for PRs and issues.
- `github2_issues` includes documents for the comments and the creation of issues.

Please rename the index patterns so their names are not counterintuitive.