feat: support for different key storages and signature services

PManaras commented 3 months ago

Description

This PR introduces support for implementing different types of keystorages via the newly KeyProvider interface. This interface can be used to retrieve keys from different types of storages, i.e. remote vaults, file-system, database.

The newly created SigningService can be used to implement different types of signature processes. The standard signature process is "LOCAL" meaning the MIW will use keys provided by the keyprovider to sign VP/VC locally.

This PR also adds to new properties to application.yaml (authoritySigningServiceType (defaults to "LOCAL), localSigningKeyStorageType (defaults to DB). These additions are also reflected in the corresponding env-files.

The database entity Wallet was updated and now contains a new field signingServiceType that reflects which wallet uses which signatureServices. The new field is introduced via a new database migration (v3) and sets the signing_service_type to "LOCAL" for all existing wallets. This means: with the standard configuration the MIW will act as before.

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