Key role syntax anomalies

Ensure we use consistent syntax and casing we use for the key roles:

    ///  * **`#[adhoc(role = "...")]`** (toplevel):
    ///    Specifies the role - the initial portion of the leafname.
    ///    This should be the name of the key in the Tor Specifications.
    //     TODO HSS casing/syntax anomalies for key role:
    //        Some keys in tor-hsservice have roles like k_..., and some KP_... or KS_...
    //        Maybe we should use `KS_...` in #[adhoc(role)], but lowercase in ArtiPaths.
    //        It'll have to become the responsibility of code here to convert.
    //        (We should include the S or P in KS_ or KP, because we might in the future
    //        want to store public keys too; actually we even do store KP_hs_id right now,
    //        but that is wrong according to the design docs.)