Blog: Convert tests to Pester 5 for a DSC Community repository (#160)

* First draft

* Fix text

* Fix text

* Add section

* More sections filled

* Add more sections

* Fix blank row

* Add section around stub modules

* Update text around verifiable mocks

* Add table of contents

* Fix some grammar

* Minor adjustment to verifiable mocks

* Fix review comments as r5

* Fix missed comments

* fix review comments at r7