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

xtask/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "xtask"
+authors.workspace = true
+description.workspace = true
+edition.workspace = true
+homepage.workspace = true
+license.workspace = true
+readme.workspace = true
+repository.workspace = true
+version.workspace = true
+
+[dependencies]
+conduwuit-admin.workspace = true
+conduwuit.workspace = true
+clap.workspace = true
+
+askama = "0.15.1"
+cargo_metadata = "0.23.1"
+
+[lints]
+workspace = true