ITransaction.AddCustomAttribute should support Array arguments

[nr-ahemsath]

The .NET agent API method ITransaction.AddCustomAttribute currently does not support values of type Array. The documentation says that unsupported types will have .ToString() called on them and treated as strings. This appears to be the current behavior; the following code:

        [Transaction]
        private static void CreateTransactionWithCustomAttributeArrayArgument(int length)
        {
            var eventAttributes = new string[length];
            for (int i = 0; i < length; i++) {
                eventAttributes[i] = $"foo{i}";
            }
            var tx = NewRelic.Api.Agent.NewRelic.GetAgent().CurrentTransaction;
            tx.AddCustomAttribute("ArrayAttributeTest", eventAttributes);
        }

results in the following atrribute attached to the transaction:
ArrayAttributeTest System.String[]

We have a customer request to support array custom attribute values "not via escaping & stringifying json & then using NRQL for parsing".

[workato-integration]

https://new-relic.atlassian.net/browse/NR-364714