Support array member names

[mpraski]

First of all thank you for this wonderful library!

I've been using it to communicate with the SES API, specifically the get_identity_verification_attributes call, and it seems that current body encoder is not handling certain requests in accordance with the spec.

The call:

AWS.SES.get_identity_verification_attributes(client, %{"Identities" => ["example.com"]})

generates following request body:

Action=GetIdentityVerificationAttributes&Identities.1=example.com&Version=2010-12-01

This results in a HTTP 400 from AWS, which happens due to the array member naming convention of having the "member" in between the array name and the index:Identities.member.1=example.com rather than Identities.1=example.com. (See https://docs.aws.amazon.com/ses/latest/APIReference/API_GetIdentityVerificationAttributes.html)

AWS CDK for e.g. Golang factors in the member name in the array format (https://github.com/aws/aws-sdk-go-v2/blob/main/aws/protocol/query/array.go#L36), and I assume the AWS.Util.encode_query_value/1 would need to be made configurable to some extent to allow those member names globally/per API.

I'll do more research on this convention and gladly raise a PR to address this issue - suggestions are welcome.

[namjae]

#199 will add member keyword and i was able to solve my problem.