add options to generate completions (#1103)

* add options to generate completions

use clap-complete crate to generate completions scripts: easytier-core --generate fish > ~/.config/fish/completions/easytier-core.fish

---------

Co-authored-by: Sijie.Sun <sunsijie@buaa.edu.cn>

Cargo.lock

@@ -1197,6 +1197,15 @@ dependencies = [
  "unicode-width 0.2.0",
 ]
 
+[[package]]
+name = "clap_complete"
+version = "4.5.55"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5abde44486daf70c5be8b8f8f1b66c49f86236edf6fa2abadb4d961c4c6229a"
+dependencies = [
+ "clap",
+]
+
 [[package]]
 name = "clap_derive"
 version = "4.5.28"
@@ -1961,6 +1970,7 @@ dependencies = [
  "chrono",
  "cidr",
  "clap",
+ "clap_complete",
  "crossbeam",
  "dashmap",
  "dbus",