Add InflationData query type

This pull request is:

[ ] A documentation error, docs update, or typographical error fix
- No tests or issue needed
[ ] A code fix
- Please reference the related issue by including "Closes <link to issue>" in this Pull Request's summary section.
  - If no issue exists, please create a bug report issue
- Please include tests. Fixes without tests will not be accepted unless it's related to the documentation only.
- Please make sure docs are updated if need be
[x] A feature implementation
- Please reference the related issue by including "Closes <link to issue>" in this Pull Request's summary section.
  - If no issue exists, please create a feature enhancement issue
- Please include tests
- Please make sure docs updates are both thorough and easy to reproduce by somebody with limited knowledge of the feature that you are submitting

Happy engineering!

tellor-io / telliot-feeds