Azure SDK for Go Samples

Add samples for MySQL flexible servers SDK (#286)

* Simple sample sceleton for mysql & postgresql

* Test basic operations

* Fixed issue with confusing git mod name between current and forked branch

* Fix typo

* Fix malformed Example_ test name

* Change sample file names. Add README.md files

* Properly delete old files, add necessary parameters for server creation

* Update README.md files

* Refactor FirewallRule call in the clients. Fix invalid name

* Update postgresql sample to reflect newest sdk changes

* Fix package names for mysql,postgresql flexible server samples

* Add the mysql samples

* Remove own go.mod dependencies

* Fix build issue