schema validate container_name with regex

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Signed-off-by: kpbaks <kristoffer.pbs@tuta.io>

Author: kpbaks

schema/compose-spec.json

@@ -206,7 +206,8 @@
         },
         "container_name": {
           "type": "string",
-          "description": "Specify a custom container name, rather than a generated default name."
+          "description": "Specify a custom container name, rather than a generated default name.",
+          "pattern": "[a-zA-Z0-9][a-zA-Z0-9_.-]+"
         },
         "cpu_count": {
           "oneOf": [