SATOSA_REQUESTED_ATTRIBUTES environment is not sufficent for all backends

[MdreW]

spid and cie use same environment for requested attributes, but cie and spid frequently don't require same attributes.
For example I can require email for SPID but not for CIE.

https://github.com/italia/Satosa-Saml2Spid/blob/2042c95ab2d1228f4d3133044667415eb6d555b6/example/plugins/backends/ciesaml2_backend.yaml#L36

https://github.com/italia/Satosa-Saml2Spid/blob/2042c95ab2d1228f4d3133044667415eb6d555b6/example/plugins/backends/spidsaml2_backend.yaml#L35

https://github.com/italia/Satosa-Saml2Spid/blob/2042c95ab2d1228f4d3133044667415eb6d555b6/Docker-compose/docker-compose.yml#L110

it might be useful to divide them