Added headers for CRR Cascaded

[SylvainSenechal]

ISSUE : CLDSRVCLT-14

Crr cascaded design : https://github.com/scality/citadel/pull/349

Related PRs :
Arsenal : scality/Arsenal#2628
Cloudserver : scality/cloudserver#6179
Backbeat : Not done yet
S3utils : Not done yet

[bert-e]

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[bert-e]

Waiting for approval

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[maeldonn]

To document errors:

/// Returned when a version of an object already exists
@error("client")
@httpError(409)
structure ConflictException {
    @required
    message: String
}

@http(method: "PUT", uri: "/_/backbeat/data/{Bucket}/{Key+}?v2")
@unsignedPayload
operation PutData {
    input: PutDataInput,
    output: PutDataOutput,
    errors: [ConflictException]
}

[SylvainSenechal]

First I added some tests, but they were too functional and not really oriented toward just testing the client itself. + we already have test testing the client itself for putData/putMetadata

So I added the test in Cloudserver : They are functional test using Cloudserver client with the micro version id, testing 409 error, actual api behavior etc. I think they are better in cloudserver than in here