Investigate excessive AWS Secrets Manager Secret Creation

[Hermann-Core]

Bug Description

A vast number of secrets are being created in AWS Secrets Manager, far exceeding the expected count for a single application instance.

Suspected Culprit

In the DID generation and initialization logic within the did-endpoint plugin:

1. Key Generation on Every Call: The didgen() function in crates/web-plugins/did-endpoint/src/didgen.rs generates new cryptographic keys (Ed25519 and X25519) every time it is invoked.
2. Unreliable Validation Trigger: The plugin's mount() function in crates/web-plugins/did-endpoint/src/plugin.rs calls didgen() if validate_diddoc() fails.
3. Transient Failure Handling: The validate_diddoc() function can fail for reasons other than a missing DID document, such as transient network errors when communicating with the keystore or the repository. When this happens during application startup, a new DID document and new keys are generated, leading to new secrets being stored in AWS Secrets Manager.

Proposed Solution

Modify the initialization logic in crates/web-plugins/did-endpoint/src/plugin.rs to only generate a new DID document if one does not already exist in the persistent storage (MongoDB).