Fix Graphql/Descriptions rubocop offences

About

!46721 (merged) has introduced a new rubocop that enforces periods at the end of GraphQL description strings.

It added the current list of offences to .rubocop_manual_todo.yml.

To do

Correct the offences and split the changes across a number of MRs in order to make it easier for reviewers.

The offences can be autocorrected using:

bundle exec rubocop --auto-correct --only Graphql/Descriptions

The offences should also be removed from the list in .rubocop_manual_todo.yml.