FEAT-Smarter migration package

[CarlosOVillanueva]

Right now, migration is one-way (Netscaler to Avi). This needs to be abstracted in the same way I abstracted the sdkfork to allow migration between any load balancer type and future load balancers.

WANT

• sdkfork implementation of migration package. This decision must be made based on the mfr value defined in the SdkTarget struct.
• The migration package will use load balancer specific ETL functions defined within virtualserver (and dependent packages) versus hard-coded ETL functions currently residing in the migration package.