Add command line option

USAGE.md

@@ -270,6 +270,10 @@ Then in `packwerk.yml`, you can set the `formatter` to the identifier for your c
 formatter: my_offenses_formatter
 ```
 
+You can also pass in a formatter on the command line:
+```
+bin/packwerk check --format=my_offenses_formatter
+```
 ### Privacy Checker
 
 [`packwerk-extensions`](https://github.com/rubyatscale/packwerk-extensions) (originally extracted from `packwerk`) can be used to help define and enforce public API boundaries of a package. See the README.md for more details. To use this, add it to your `Gemfile` and then require it via `packwerk.yml`:

lib/packwerk/cli.rb

@@ -182,6 +182,7 @@ def list_validation_errors(result)
     def parse_run(params)
       relative_file_paths = T.let([], T::Array[String])
       ignore_nested_packages = nil
+      formatter = @offenses_formatter
 
       if params.any? { |p| p.include?("--packages") }
         OptionParser.new do |parser|
@@ -195,11 +196,19 @@ def parse_run(params)
         ignore_nested_packages = false
       end
 
+      if params.any? { |p| p.include?("--format") }
+        OptionParser.new do |parser|
+          parser.on("--format=FORMATTER", String, "name of formatter to use") do |formatter_identifier|
+            formatter = OffensesFormatter.find(formatter_identifier)
+          end
+        end.parse!(params)
+      end
+
       ParseRun.new(
         relative_file_set: fetch_files_to_process(relative_file_paths, ignore_nested_packages),
         configuration: @configuration,
         progress_formatter: @progress_formatter,
-        offenses_formatter: @offenses_formatter
+        offenses_formatter: formatter
       )
     end
   end