Revisit ignored solhint rules for 6.0.0

[iansuvak]

Context and scope
To support update to our unpinned solhint dependency we've explicitly turned off most of the new rules. We should revisit if we want to add any of them back and which ones.

A particular example of a useful one would be "use-natspec"

Discussion and alternatives

Open questions

[geoff-vball]

I think gas-struct-packing would be useful iff we're able to ignore specific old contracts. We should not go around changing the order of struct fields in our upgradeable contracts :)