register with optional role in the post request

server/src/auth/docs/role_added.txt

@@ -0,0 +1,37 @@
+❯ grpcurl -plaintext -d '{
+  "username": "testuser_default_role",
+  "email": "default@example.com",
+  "password": "password",
+  "password_confirmation": "password"
+}' localhost:50051 multieko2.auth.AuthService/Register
+{
+  "id": "73017288-af41-49d8-b4cb-2ac2109b38a1",
+  "username": "testuser_default_role",
+  "email": "default@example.com",
+  "role": "accountant"
+}
+❯ grpcurl -plaintext -d '{
+  "username": "testuser_admin_role",
+  "email": "admin@example.com",
+  "password": "password",
+  "password_confirmation": "password",
+  "role": "admin"
+}' localhost:50051 multieko2.auth.AuthService/Register
+{
+  "id": "9437e318-818b-4c34-822d-c2d6601b835e",
+  "username": "testuser_admin_role",
+  "email": "admin@example.com",
+  "role": "admin"
+}
+❯ grpcurl -plaintext -d '{
+  "username": "testuser_invalid_role",
+  "email": "invalid@example.com",
+  "password": "password",
+  "password_confirmation": "password",
+  "role": "invalid_role_name"
+}' localhost:50051 multieko2.auth.AuthService/Register
+ERROR:
+  Code: InvalidArgument
+  Message: Invalid role specified: 'invalid_role_name'
+╭─     ~/Doc/pr/multieko2/server     main +3 !1 
+╰─