Use go:embed from go 1.16 to store OPA policies in separate files

[denis-tingaikin]

Motivation

With go 1.16 we can use files from the project. Look at https://golang.org/pkg/embed/

Currently, OPA policies are storing as strings. So now we can move them into separate files to make it easy to find/edit and to reduce the complexity of the go files.

[denis-tingaikin]

@edwarnicke Also https://golang.org/pkg/embed/ can be used for vpp configs :)

[edwarnicke]

@denis-tingaikin Yes :)