feat: Add refresh token expiration and rotation settings

cmd/dex/config.go

cmd/dex/serve.go

examples/config-dev.yaml

server/handlers.go

server/rotation.go

server/rotation_test.go

server/server.go

server/server_test.go

storage/conformance/conformance.go

storage/etcd/types.go

storage/kubernetes/types.go

storage/sql/crud.go

storage/sql/migrate.go

storage/storage.go