chore(tests): Zms 86 mailboxes (#501)

* added new file to test git repo setup

* added mailboxes tests part 1, POST to /users/{user}/mailboxes

* mailboxes tests GET /users/{user}/mailboxes

* remove .only

* fix returned value check

* remove text.txt. Fix mailboxes-test.js test run name

* fix GET request tests. Add tests for GET /users/{user}/mailboxes/{mailbox}

* added tests for PUT /users/{user}/mailboxes/{mailbox}

* added couple more PUT tests. Added tests for DELETE /users/{user}/mailboxes/{mailbox}. Fixed namings in some places

* remove unnecessary .send(), add generated md file to gitignore

* add new line to gitignore

.gitignore

@@ -7,3 +7,4 @@ config/development.*
 certs/test-*
 zmta-milter
 zmta-milter.toml
+api-tests-overview.md