Add CLI flag for HTTP API token path (VC) (#6577)

* Add cli flag for HTTP API token path (VC)

* Add http_token_path_flag test

* Add pre-check for directory case & Fix test utils

* Update docs

* Apply review: move http_token_path into validator_http_api config

* Lint

* Make diff lesser to replace PK_FILENAME

* Merge branch 'unstable' into feature/cli-token-path

* Applt review: help_vc.md

Co-authored-by: chonghe <44791194+chong-he@users.noreply.github.com>

* Fix help for cli

* Fix issues on ci

* Merge branch 'unstable' into feature/cli-token-path

* Merge branch 'unstable' into feature/cli-token-path

* Merge branch 'unstable' into feature/cli-token-path

* Merge branch 'unstable' into feature/cli-token-path

book/src/help_vc.md

@@ -69,6 +69,10 @@ Options:
           this server (e.g., http://localhost:5062).
       --http-port <PORT>
           Set the listen TCP port for the RESTful HTTP API server.
+      --http-token-path <HTTP_TOKEN_PATH>
+          Path to file containing the HTTP API token for validator client
+          authentication. If not specified, defaults to
+          {validators-dir}/api-token.txt.
       --log-format <FORMAT>
           Specifies the log format used when emitting logs to the terminal.
           [possible values: JSON]