refactor accessing registry configs via drivers

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/util/resolver/config/config.go

@@ -0,0 +1,15 @@
+package config
+
+type RegistryConfig struct {
+	Mirrors      []string     `toml:"mirrors"`
+	PlainHTTP    *bool        `toml:"http"`
+	Insecure     *bool        `toml:"insecure"`
+	RootCAs      []string     `toml:"ca"`
+	KeyPairs     []TLSKeyPair `toml:"keypair"`
+	TLSConfigDir []string     `toml:"tlsconfigdir"`
+}
+
+type TLSKeyPair struct {
+	Key         string `toml:"key"`
+	Certificate string `toml:"cert"`
+}