NAT-328: added validation for site name

gso/api/v1/imports.py

 import ipaddress
 from typing import Any
 from uuid import UUID
+import re
 
 from fastapi import Depends, HTTPException, status
 from fastapi.routing import APIRouter
@@ -104,6 +105,15 @@ class IptrunkImportModel(BaseModel):
 
         return value
 
+    @validator("site_name", allow_reuse=True)
+    def site_name_must_be_valid(cls, site_name: str) -> str:
+        # Accept 3 chapital letters and only one ditigt after capital letters.
+        pattern = re.compile(r"^[A-Z]{3}[0-9]?$")
+        if not bool(pattern.match(site_name)):
+            raise ValueError(f"Enter a valid site name similar looks like AMS, AMS1or LON9. Get: {site_name}")
+
+        return site_name
+
     @root_validator
     def check_members(cls, values: dict[str, Any]) -> dict[str, Any]:
         min_links = values["iptrunk_minimum_links"]