Revise expiration delays for signed entity types

[jpraynaud]

Why

The timeout of the signed entity types should be optimized based on current certification delay and in order to avoid blocking the signature of some entity types. In particular, the CardanoImmutableFilesFull never expires and thus blocks the CardanoDatabase and CardanoTransactions. Also the MithrilStakeDistribution never expires which limits the resilience of the certification in the case of being unable to create a certificate for this signed entity type (even though the probability of such an occurrence is very low).

What

Revise and update the timeouts of the signed entity types:

        match self {
            Self::MithrilStakeDistribution(_) => Some(Duration::from_secs(3600)),
            Self::CardanoImmutableFilesFull(_) => Some(Duration::from_secs(600)),
            Self::CardanoStakeDistribution(_) => Some(Duration::from_secs(1800)),
            Self::CardanoTransactions(_, _) => Some(Duration::from_secs(600)),
            Self::CardanoDatabase(_) => Some(Duration::from_secs(600)),
        }

How

• Update the timeouts of the signed entity types

Later

• Re-revise the timeouts another time?
• Remove the capability of a signed entity type to never expire?