espflash split config migration

[MabezDev]

If a user has a global config with port info from espflash v3, it is currently ignored on main. We should either make the user aware of this, or handle the migration (i.e the split of the files) for them.

[SergioGasquez]

What about checking if the project configuration has port configuration(s) on it, and if it does, we throw and error and point to a "migration guide" or we just explain this in the error?

[MabezDev]

I think the old config is just this right?

#[derive(Debug, Deserialize, Serialize, Default, Clone)]
pub struct OldConfig {
    /// Project configuration
   #[serde(flatten)]
    pub project_config: ProjectConfig,
    /// Port configuration
    #[serde(flatten)]
    pub port_config: PortConfig,
}

I wonder if we should just try and load as an old config (or if we can easily see if there is a [ports] section in the project file), if we do that, that next time we save the config(s) it should be in the correct place without the user having to do anything?

I'm not that familiar with the config system though, and maybe the multiple locations of the files complicates things here.

What do you think?