Issues upgrading to 3.4

[jsmcnair]

Hi.

I had a few issues migrating to v3.4 and wanted to share my experience. I can submit fixes for these if necessary.

We are using DCT validators against private containers. The first issue I experienced was that the file name required for the repository credentials has change to secret.yaml but this has not yet been reflected in the documentation:

connaisseur/docs/validators/notaryv1.md

Line 188 in 6ca19ae

| `auth.secretName` | - | - | (Preferred over `username` + `password` combination.) Name of a Kubernetes secret that must exist in Connaisseur namespace beforehand. Create a file `auth.yaml` containing:<br/>&nbsp; `username: <user>` <br/>&nbsp; `password: <password>` <br/>Run `kubectl create secret generic <kube-secret-name> --from-file auth.yaml -n connaisseur` to create the secret.|

Also when providing the public key I did not update value to include the headers (e.g. BEGIN PUBLIC KEY), which I found caused a panic in connaisseur when trying to decode the trust root key. I think it's because the the pem.Decode method returns nil if it doesn't find a key so x509.ParsePKIXPublicKey gets passed a nil pointer:

connaisseur/internal/validator/notaryv1/notaryv1_validator.go

Line 217 in 6ca19ae

pubDecode, rest := pem.Decode([]byte(tr.Key))

. Once I updated the key format being passed to the application configuration the nil pointer panic went away, but I feel this should be checked for and properly handled in the code.

[phbelitz]

thank you for your feedback!

I created a PR to fix this: #1624