docs(docs-infra): fix wrong links in first-app-lesson-14.md
in first-app-lesson-14.md, the links to starting code point to the wrong lesson 06 instead of lesson 13 and the links to completed code point to lesson 07 instead of lesson 14
PR Close#51097
Adds the content for lesson 13, fixes some code inconsistencies for the services code in the examples, and adds this lesson to the navigation.
PR Close#49980