feat: flag and config to skip notifications by jlucktay (#5)

* feat: flag and config to skip notifications

At the end of a run, topgrade normally sends a system notification.
This change adds a command-line flag and a config-file option to
disable this behaviour.

* fix: clippy issues

Also derive Eq where PartialEq is being derived.
https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

Authored-by: James Lucktaylor <jlucktay+github@gmail.com>
Approved-by: Thomas Schönauer <t.schoenauer@hgs-wt.at>

Cargo.lock

@@ -1834,7 +1834,7 @@ dependencies = [
 
 [[package]]
 name = "topgrade"
-version = "9.0.1"
+version = "9.1.0"
 dependencies = [
  "anyhow",
  "cfg-if",