gRPC-server won't start with two services

[magento-engcom-team]

Description:
gRPC server won't start with few services

Steps to reproduce:

1. install magento with storefront
2. install all required extension to run grpc-server, see app/code/Magento/Grpc/README.md or https://github.com/duhon/magento-docker/blob/a8196a5cae08fd830f659553613315e57d781956/README.md if you use DebBox
3. In readme files the following CLI command is used:

bin/magento storefront:grpc:init \\Magento\\CatalogStorefrontApi\\Api\\CatalogProxyServer
{code}

Stop grpc-server and run the command with 2 parameters:

{code}
bin/magento storefront:grpc:init \\Magento\\CatalogStorefrontApi\\Api\\CatalogProxyServer  \\Magento\\CatalogStorefrontApi\\Proto\\VariantServiceInterface
{code}
 
(/) Expected:
gRPC server started successfully without errors
{code}
root@app:/var/www/magento2ce# ./vendor/bin/grpc-server 
DEBU<0000] [metrics]: disabled                          
DEBU[0000] [rpc]: started                               
DEBU[0000] [grpc]: started    
{code}

(x) Actual
gRPC server stops after start 
{code}
root@app:/var/www/magento2ce# ./vendor/bin/grpc-server 
DEBU[0000] [metrics]: disabled                          
DEBU[0000] [rpc]: started                               
DEBU[0000] [grpc]: started                              
ERRO[0000] [grpc]: [grpc]: unable to connect to worker: invalid data found in the buffer (possible echo): signal: killed 
DEBU[0000] [rpc>: stopped  

(!) Notes:
try to run with Magento\CatalogStorefrontApi\Api\VariantServiceProxyServer. Probably the issue is with this service.

[magento-engcom-team]

The issue was exported from the internal JIRA. The link to the original JIRA issue: https://jira.corp.magento.com/browse/SFAPP-99

[m2-assistant]

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[RuslanKostiv1]

checked this with new variants service and looks we can use 2 and more services:

bin/magento storefront:grpc:init \\Magento\\CatalogStorefrontApi\\Api\\CatalogProxyServer \\Magento\\CatalogStorefrontApi\\Api\\VariantServiceProxyServer

see #357