Prior to this commit, the SQL fragments included variables that were set
configured at a global level.
With this commit, we're now saying that each lever "knows" what variable
it needs; and providing the means at lever declaration time to "say"
what those variable names are. (e.g. `Articles::Feeds::LEVER_CATALOG`).
Then as part of the variant configuration (in the
`./config/feed-variants/*.json` files) we now include the expected value
of those parameters; which by convention (and coercion) are integers.
This relates to forem/forem#17584 because we want to move from a
privileged user reaction that has two values (`negative` and `positive`)
into four values (`very_negative`, `negative`, `positive`, and
`very_positive`). To do that, we'll create a new lever; but that's for
another pull request.
38ee9ef309