Consider supporting parameterized queries

[iaindillingham]

opensafely/winter-pressures could benefit from a parameterized query, to move the values of @study_start_date and @study_end_date into project.yaml.

[iaindillingham]

Similarly, opensafely/ons-cis-short-data-report could use them such that we don't have to copy the same query each time we want to count the values in a categorical column.