Make parsing of TOML configurations strict (server + ckms)

[Manuthor]

There is a fault-tolerance in both TOML configurations that should be forbidden to avoid false-positive.
If a field is unknown, it must exist early.

[HatemMn]

I can trivially fix this. The question is more about "why do we want this ?", it will make the KMS more annoying to start without a proper end-user benefit. Maybe the goal is to reduce attack surface ?

Anyway, Serde has already a built-in way of doing what's required and the file crate/server/src/main.rs has already a pretty good test for the TOML

@Manuthor if you really want to implement this, add me a simple 'example' with a 'before OK' -> 'after NOT_OK' , and I will take this PR