docs: HOWTO for cloud devops + update TEST_STAND manifests for new API Gateway

- HOWTO_IMPLEMENT_NEW_CLOUD_SERVICE.md: rules for implementing new managed services
  (naming, params, map-fixed blocks, operations, subresources, validation, checklist)
- HOWTO_ADD_NEW_SERVICE.md: how to add service to terraform provider pipeline
- TEST_STAND/*/main.tf: version 5.0.57, api_endpoint -> lk-api-gateway-test
- TEST_STAND/POSTGRES/resources.tf: rewritten for new map-fixed param structure

TEST_STAND/MARIA_DB/main.tf

@@ -2,7 +2,7 @@ terraform {
   required_providers {
     nubes = {
       source  = "terra.k8c.ru/nubes/nubes"
-      version = "2.0.8"
+      version = "5.0.57"
     }
   }
 }
@@ -15,6 +15,6 @@ variable "api_token" {
 
 provider "nubes" {
   api_token    = var.api_token
-  api_endpoint = "https://deck-api-test.ngcloud.ru/api/v1/index.cfm"
+  api_endpoint = "https://lk-api-gateway-test.ngcloud.ru/api/v1/svc"
 }