Merge typed role and rolegroup configs before converting to product-config maps

[nightkr]

Currently, overriding gets pretty tricky, since reasonable-looking code like this:

#[derive(Deserialize)]
struct FooConfig {
    #[serde(default = "FooConfig::default_port")]
    port: u16,
}

impl FooConfig {
    fn default_port() -> u16 {
        9191
    }
}

is subtly wrong, since the rolegroup's default port will override an explicitly specified role-level port. #282 made this somewhat worse, since it now triggers for all rolegroups (whereas previously it would only trigger for rolegroups that specified a config: field), but the issue was still there before.

[lfrancke]

@teozkr could you please add a link / quick explanation what this is blocked on?
Something in schemars if I'm correct

[lfrancke]

@teozkr ping

[nightkr]

Ah sorry, @lfrancke. This is blocked on GREsau/schemars#167, which is required in order to set up the correct type bounds in the generated schemas.

[lfrancke]

If we don't get any feedback here, is there anything we can reasonably do?
e.g. ping one last time and let him know that we'll get started on our own PR starting from his draft?