LMS-1102 Add document check - footnote UKPGA citations

Summary of feature request

Add a validation rule (Document check) to identify incorrectly formatted chapter numbers in citations within footnotes. They should be “c. [num]” with a single space between the chapter abbreviation and the number, e.g. “c. 3” or “c. 25”.

Original user description

This story is to add an mandatory document check for footnote text.

The error should be triggered when drafters cite UKPGA chapter numbers in footnotes as “c.[XX]” instead of “c. [XX]”. For example, “2022 c.16” should be “2022 c. 16”.

Suggested warning text: “A citation of a UKPGA chapter number should be in the format "c. XX", with a space between the chapter abbreviation and the number.”