feat: Improve admin command reference generation

- Change xtasks to use `clap` for argument parsing
- Generate admin command reference manually instead of with `clap_markdown`
- Split admin command reference into multiple files

.vscode/settings.json

@@ -7,6 +7,5 @@
         "continuwuity",
         "homeserver",
         "homeservers"
-    ],
-    "rust-analyzer.cargo.features": ["full"]
+    ]
 }