Export gensign failure otel metrics

[py4chen]

To capture authn or any handler signing failure for gensign.

❯ ssh -A user_a@localhost -p 222 -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no \
'{"ifVer":7, "username":"user_invalid", "hostname":"localhost", "sshClientVersion":"0.0"}'
Warning: Permanently added '[localhost]:222' (ECDSA) to the list of known hosts.
{"level":"info","app":"gensign","id":"b7683c0d3a","err":"paranoids.regular handler authentication error, cannot sign the challenge: agent: failed to sign challenge","handler":"paranoids.regular","time":"2024-11-18T15:31:38Z","caller":"/go/src/github.com/theparanoids/ysshra/gensign/gensign.go:38","msg":"authentication failed"}
{"level":"error","app":"gensign","id":"b7683c0d3a","id":"b7683c0d3a","err":"all authentications failed, all authentications failed","time":"2024-11-18T15:31:38Z","caller":"/go/src/github.com/theparanoids/ysshra/cmd/gensign/main.go:127","msg":"failed to run gensign"}

# HELP ysshra_gensign_run_total Count the number of gensign runs
# TYPE ysshra_gensign_run_total counter
ysshra_gensign_run_total{gensign_error_type="1",job="gensign"} 1


# HELP ysshra_gensign_total Count the number of gensign runs
# TYPE ysshra_gensign_total counter
ysshra_gensign_run_total{gensign_error_type="7",job="gensign"} 1```

<!-- The following line must be included in your pull request -->
I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.