[Version-unspecific] ConstantName .String() for Constants strings #check-lint-warning

[Version-unspecific]

Intended for #1966
'Duplicate string literals for all keys and substrings should reference a single constant'.

This Merge Request is intended to be ConstantName-specific
(terms in
https://gitlab.com/thorchain/thornode/-/blob/develop/constants/constant_values.go
, which can be (though are not if no constants_v1.go value is assigned) reflected in
https://thornode-v1.ninerealms.com/thorchain/constants )
without overlapping with Mimir-only-keys Merge Request !3561
'Consolidated Mimir-only key string constants #check-lint-warning'.

Neither MR should be able to close the Issue by itself.

This is intended to be exhaustive (only avoiding regression tests as they use .yaml files rather than .go),
but please tell me if I have missed something.