Make the URL and Repo FQRN CLI args optional

They are no longer mandatory as they might be specified through the
config file(s). Now to go assemble that config and fix the compiler
errors.

src/cli.rs

@@ -4,9 +4,9 @@ use clap::{Parser, Subcommand};
 #[command(version, about, long_about = None)]
 pub struct Args {
     #[arg(short = 'u', long = "url", env = "GTTOOL_GITEA_URL")]
-    pub gitea_url: String,
+    pub gitea_url: Option<String>,
     #[arg(short = 'r', long = "repo", env = "GTTOOL_FQRN")]
-    pub repo: String,
+    pub repo: Option<String>,
 
     #[command(subcommand)]
     pub command: Commands,