Insights error handling for config file reading

To allow a better experience when using insights we could check the insights config file when it is loaded after a request from the frontend. The current problem with the config file can then be displayed to the user

• Check file formatting
  • Valid yml
  • Valid fields
• Check chart types
• Check query types

The insights frontend will display a message field from the payload in case of an unsuccessful request:

• https://gitlab.com/gitlab-org/gitlab-ee/commit/f9630308280bec7147bbf6087cd91e7647d03c10#881ef80f7b03d5daab630e5db6cf3400b3d4a231_20_18