Support mounted proto directories to docker

[Neytronik]

Protocols can have nested classes from other directories

and when trying to connect only one proto file to the mock, we get a nested imports error

Version: 3.5.1

Expected behavior

for imports
import "google/protobuf/empty.proto";
import "google/protobuf/timestamp.proto";
import "validate/validate.proto";

when we mounted this directories to mockingbird image, then mock can be created

Actual behavior

error
on UI
java.io.FileNotFoundException: /tmp/temp734059700379678195/descriptor.desc (No such file or directory)

on Back
validate/validate.proto: File not found.
requests.proto:7:1: Import "validate/validate.proto" was not found or had errors.

@mockingbird/maintainers