Allow interpret keys as native list, not just CSV string

[JWCS]

Currently keys are treated as CSV strings, ex

creation_rules:
    - pgp: >-
        85D77543B3D624B63CEA9E6DBC17301B491B3F21,
        FBC7B9E2A4F9289AC0C1D4843D16CEE4A27381B4

I've been bitten by two problems recurringly with this format.

1. Comments aren't allowed in yaml block scalar form. It's hard to add metadata (ex, this is the semantic identity of this key), without comments.
2. There's an annoying error when there's a trailing comma on the last element, "" isn't a valid key. This could ofc be itself fixed... but it's symptomatic of not using a native list format, but deferring to a secondary parser and syntax. This is especially the case when the keys might be auto generated, moved around, etc...

Ex

creation_rules:
    - pgp:
        - 85D77543B3D624B63CEA9E6DBC17301B491B3F21 # name@email.com
        - FBC7B9E2A4F9289AC0C1D4843D16CEE4A27381B4 # server_XZY

Note: this shouldn't be a breaking change, so long as its a loosening of the restrictions; ie typeof(pgp) == string | list<string>

[felixfontein]

Duplicate of #845.