The user should be able to customize the diff table labels from the environment

[NyanKiyoshi]

Is your feature request related to a problem? Please describe. Users might get confused by the left and right label, because those labels might make sense for some users but not to all of them. What is left? What is right?

Describe the solution you'd like As it might be considered as a major change to actually rename those fields, it would be just easier to let the user decide what they want as label using environment variables.

DJ_QUERIES_LEFT_LABEL = "before"
DJ_QUERIES_RIGHT_LABEL = "after"