Multi-network for Remote contract import.

[geofmureithi]

Is your feature request related to a problem? Please describe.
Currently remote cross contract import only supports OCI. The community wants more sources of contracts.

• Network
• Direct path

Describe the solution you'd like
I should be able to import via alternative methods

Describe alternatives you've considered
N/A

Additional context
https://discord.com/channels/897514728459468821/1177272905780973568

[geofmureithi]

Currently, OCI works like this:

voting = "ghcr.io/eigerco/nebula/contracts/voting:v0.2.0"

This is also valid:

voting = { reference = "ghcr.io/eigerco/nebula/contracts/voting:v0.2.0", digest="sha" }

Improvements can be done:

#[derive(Debug, Serialize, Deserialize, Clone)]
#[serde(untagged)]
pub enum Contract {
    NoDigest(String),
    WithDigest {
        digest: Option<String>,
        reference: String,
    },
  Network(todo!()),
  Fs(PathBuf)
}