Conform to request data model spec 2.0

[YufengXin]

https://docs.google.com/document/d/1YKIvNgOaoSA30coT0hvhjVGb8KSu5bNxz3fbfdOBdUY/edit?usp=sharing

1. It seems to me the only change to be made is the connectionhandler:

https://github.com/atlanticwave-sdx/datamodel/blob/87d2811d02b340aee0578411b8d0cd069f726484/src/sdx_datamodel/parsing/connectionhandler.py#L33

and #L34

ie, we keep internal models as they are.

2.. see if we could close following related issues:

63

87

95

108