Enable serde(deny_unknown_fields) for config structs

[hakoerber]

Right now, the configuration files can contain additional keys without problems, they are just ignored. This is good for backwards compatibility during development, but can lead to confusing situation (e.g. when mistyping a key).

Enabling #[serde(deny_unknown_fields)] for those structs would reject those configuration files.

• Enable the setting
• Check the error codes

The errors are very unhelpful:

grm repos sync config -c ~/grm.toml
[✘] Error parsing configuration file "grm.toml": data did not match any variant of untagged enum Config