Add minitest assert_perform_linear_number_of_queries

[caalberts]

What is the purpose of this pull request?

Add linear query assertion to minitest

What changes did you make? (overview)

Is there anything you'd like reviewers to focus on?

Checklist

• [x] I've added tests for this change
• [x] I've added a Changelog entry
• [x] I've updated a documentation

[caalberts]

@palkan I have added the minitest assertion for linear queries. Please have a look.

[Earendil95]

I'll release a new version soon