Improved logging for debugging offline attestation

[hgowda-amd]

Added clear logs for when:

1. we use offline vs KDS certs.
2. Was the reference value fetched from RVPS
3. which claims are matched and which failed to match.
4. Attestation failed vs success
5. which policy was used for attestation.

[amd-aliem]

We can add the Display trait to VCEKSource to avoid having to do this match multiple times:

impl std::fmt::Display for VCEKSource {
   fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
      <put the match here>
}

https://doc.rust-lang.org/std/fmt/trait.Display.html

Then in these debugs you can just pass the variable

[amd-aliem]

This might be more opinion/personal, but I'm not certain the community will be into adding this much debug - especially for the success cases I think it's a bit excessive, based on what the rest of the repo does. I think the extra one for user-passed certs is useful, and enriching with more specific data is useful, but I think maybe evaluate some of these other ones if they are really needed?

[hgowda-amd]

agree. Now that i think of it, success messages might be redundant.

[amd-aliem]

Just a small conciseness suggestion, and the CI is failing (I think you need to do a clippy run or something), but looks good!

[amd-aliem]

I'm pretty sure this full hw_id is already shown in the logs (when fetching the KDS URL the hwid is in the path, and probably also in the attestation report as well). The comment somewhat implies it's for a security reason, which is why I'm pointing it out?

Also I think this debug that you added in the parent function above already covers the success case:

if let Ok(vcek_bytes) = result {
                debug!("fetched vcek from {:?}", source);
                info!("VCEK fetched successfully from {}", source);
                return Ok(vcek_bytes);
            }

So you can probably just add debug for the failure case here to avoid adding a lot of lines of debug code:

let vcek_path = format!("{}/vcek/{}/vcek.der", path, hw_id);
std::fs::read(&vcek_path)
      .inspect_err(|e| debug!("VCEK offline store miss: {vcek_path}: {e}"))
      .with_context(|| format!("Failed to read VCEK from {vcek_path}"))