Support SubdocArrayInsert + doc_flag::Add for MultiMutation

// @todo: This test fails because doc_flag::Mkdoc is invalid with ArrayInsert (

//  the test fails at validation for ArrayInsert with "Invalid arguments")

//  By changing to doc_flag::Add (which is valid for ArrayInsert) the test

//  gets to the execution of ArrayInsert but is fails with

//  SubdocMultiPathFailure.

//  Specific and simple (single-path) tests on ArrayInsert suggests that we may

//  have some existing issue in that area that we should address in a dedicated

//  patch.

TEST_P(XattrNoDocTest,

       DISABLED_AddUserXattrToNonExistentItemMultipathArrayInsert) {

    BinprotSubdocMultiMutationCommand cmd(

            name,

            {{ClientOpcode::SubdocArrayPushFirst,

              SUBDOC_FLAG_XATTR_PATH,

              "array",

              "0"},

             {ClientOpcode::SubdocArrayInsert,

              SUBDOC_FLAG_XATTR_PATH,

              "array.[0]",

              "1"}},

            doc_flag::Mkdoc | doc_flag::CreateAsDeleted);

    auto resp = subdocMultiMutation(cmd);

    EXPECT_EQ(cb::mcbp::Status::SubdocSuccessDeleted, resp.getStatus());

    resp = subdoc_get("array", SUBDOC_FLAG_XATTR_PATH, doc_flag::AccessDeleted);

    ASSERT_EQ(cb::mcbp::Status::SubdocSuccessDeleted, resp.getStatus());

    EXPECT_EQ("[0,1]", resp.getValue());

}