docs: explain that a misspelt v7.0.0 customers parameter is an attribute filter

obp-api/src/main/scala/code/api/v7_0_0/Http4s700Customers.scala

@@ -153,6 +153,11 @@ object Http4s700Customers {
        |sort_by, and names starting with obp_ or _. Apart from limit, offset and sort_direction (lower case)
        |they are accepted and ignored, as in v6.0.0.
        |
+       |Every other query parameter is an attribute filter, so a misspelt name is not refused: it filters by an
+       |attribute of that name. For example, `?limt=10` asks for the Customers with an attribute `limt` whose
+       |value is `10`. That usually matches no Customer, and the answer is an empty list, not an error. Check
+       |the spelling of limit, offset and sort_direction when a call returns no Customers.
+       |
        |A single value of a parameter whose name ends in currency or currency_code that looks like a currency
        |code is upper-cased by OBP-API before it is matched, as on every endpoint; comma-separated values are
        |matched as given.

obp-api/src/test/scala/code/api/v7_0_0/CustomersAtOneBankV700Test.scala

@@ -114,6 +114,15 @@ class CustomersAtOneBankV700Test extends V600ServerSetup {
         "sort_by" -> "name", "obp_limit" -> "10", "_" -> "123") should equal(List(matching))
     }
 
+    scenario("A misspelt parameter name is taken for an attribute name, so it matches no Customer instead of failing", CustomersAtOneBank, VersionOfApi) {
+      val tag = generateUUID().take(6)
+      val matching = customer("organisation_kind" -> s"bank-$tag")
+      ids("organisation_kind" -> s"bank-$tag") should equal(List(matching))
+      // limt is not limit: it is a filter on an attribute named limt, which no Customer has.
+      ids("organisation_kind" -> s"bank-$tag", "limt" -> "10") should equal(Nil)
+      ids("limt" -> "10") should equal(Nil)
+    }
+
     scenario("sort_direction orders the matching Customers by customer_id, DESC by default, and pages follow that order", CustomersAtOneBank, VersionOfApi) {
       val tag = generateUUID().take(6)
       val created = (1 to 3).map(_ => customer("cohort" -> s"s-$tag")).toList.sorted