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

Cargo.toml

@@ -1,6 +1,6 @@
 [workspace]
 resolver = "2"
-members = ["src/*", "xtask/*"]
+members = ["src/*", "xtask/"]
 default-members = ["src/*"]
 
 [workspace.package]