keyringctl:
Change `persist_direct_sigs()` to track a sig_type parameter in its
signature so that the output directory of the direct signatures can be
altered.
Change `convert_certificate()` to set a `direct_revocations` variable,
that is used to track KeyRevocations for root keys. Extend the logic to
make use of `add_packet_to_direct_sigs()` to set a list of
KeyRevocations for a given root key. Eventually call
`persist_direct_sigs()` with `direct_revocations` and a custom
`sig_type` to persist the revocation certificates.
keyringctl:
Rename `persist_direct_keys()` to `persist_direct_sigs()` as it is now
not only handling the persistence of DirectKeys but also *Certifications
directly on a root key (those without an explicit User ID).
Add inline function `add_packet_to_direct_sigs()` to
`convert_certificate()` to generically add direct signatures on a root
key, grouped by issuer.
Change `convert_certificate()` to add Certifications on a root key
(without a specified User ID) to the list of direct_sigs, so that they
are persisted alongside any existing DirectKeys.
Remove breakpoints from `persist_certifications()` as they are no longer
reached. The function is now solely used for Certifications on User IDs.
keyringctl:
Add `persist_basic_key()`, `persist_direct_keys()`,
`persist_certifications()` and `persist_revocations()` to allow for
dedicated writing of basic key material, direct key signatures,
per UID certificates and per UID revocations (respectively).
Change `convert_certificate()` to call the new dedicated write functions
instead of implementing the functionality.
Change `convert_certificate()` to raise on missing current_packet_key
when trying to work on signature files (this is unlikely to occur,
unless the input data is somehow broken, but it keeps the linter happy).
Change `convert_certificate()` to handle direct_keys by issuer on a
given root key (DirectKey signatures by the same issuer are combined).
Change the argparse subparser for the 'convert' command to include a
help text.
As the SKS infrastructure is offline for good, we need to switch to
keyserver.ubuntu.com for the time being.
The Ubuntu keyservers to not support EC keys, thus we have to ignore
failure when refreshing keys.
