Legacy MySQL 2020-01-01

[mbfrahry]

This PR adds legacy 2020-01-01 mysql to pandora. Not sure if this is the right way to do this but it's what we need to migrate mysql over to go-azure-sdk

API Specs for reference https://github.com/Azure/azure-rest-api-specs/tree/7c50841aadb4bfc241de3f09146e1f97ce3583b2/specification/mysql/resource-manager/Microsoft.DBforMySQL/legacy/stable/2020-01-01

[tombuildsstuff]

Looks like we might also need the two older versions here, although would the newer API versions work?

 $ cd vendor/github.com/Azure/azure-sdk-for-go/services/mysql/mgmt/2020-01-01/mysql
 $ grep -h -R "APIVersion = " | sort | uniq
	const APIVersion = "2017-12-01"
	const APIVersion = "2018-06-01"
	const APIVersion = "2020-01-01"

[mbfrahry]

I just poked through those apis and they only hold stuff that we aren't using so hopefully we don't need it