fix(cli): restore --help support by enabling clap's help feature explicitly (#540)

- In clap v4, the feature system was restructured to be fully granular
- With default-features = false, **no features** are enabled, including help
- Previously in v3, help output was always included by default
- Without explicitly enabling the help feature, running:
    ./linkerd-network-validator --help
  results in:
    error: unexpected argument found
- This commit adds the help feature back to enable standard CLI help text

Ref: https://github.com/clap-rs/clap/blob/master/CHANGELOG.md#400---2022-09-28

Signed-off-by: Debasish Biswas <debasishbsws.dev@gmail.com>

Author: debasishbsws

validator/Cargo.toml

@@ -16,7 +16,7 @@ tracing = "0.1"
 [dependencies.clap]
 version = "4"
 default-features = false
-features = ["derive", "env", "std"]
+features = ["derive", "env", "std", "help"]
 
 [dependencies.tokio]
 version = "1"