feat: add examples of unit tests

feat: add solution of homework - ApiApplication

Merge pull request #1 from AndrewBynkov/patch-1

feat: add useful articles of dotnet

fix: misprint

feat: examples of lesson 9

feat: add solution of homework - FitnessTracker

feat: add dto additional task

docs: add screenshots to homeworks documentation

docs: update homeworks documentation

fix: delete unnecessary files

refactor: replace lessons to a separate folders

refactor: replace homeworks to a separate folder

docs: add list of additional tasks

docs: add list of useful articles of dotnet