feat: add optional filepath argument to run command

[zimeg]

Changelog

The run command now accepts an optional argument for the app entry point:

$ slack run ./src/app.py

Summary

This PR adds an optional filepath argument to the run command.

Preview

Current and continued behavior:

With a path argument provided:

When the file doesn't exist:

Reviewers

The following commands shows the optional argument of a filepath for the run command:

$ slack create asdf -t slack-samples/bolt-js-starter-template
$ cd asdf
$ slack run         # No argument defaults to the start hook
$ slack run app.js  # The common path appears to be alright

$ mkdir src
$ mv app-oauth.js src

$ slack run src/app-oauth.js  # Find a SDK runtime error!
$ slack run src/example.js    # Find the file not found

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

❌ Patch coverage is 57.89474% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.59%. Comparing base (5122e45) to head (bc64865).

Files with missing lines	Patch %	Lines
internal/pkg/platform/localserver.go	0.00%	7 Missing ⚠️
internal/pkg/platform/run.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                   @@
##           zimeg-fix-env-quote     #417      +/-   ##
=======================================================
- Coverage                68.62%   68.59%   -0.04%     
=======================================================
  Files                      218      218              
  Lines                    18164    18177      +13     
=======================================================
+ Hits                     12465    12468       +3     
- Misses                    4539     4545       +6     
- Partials                  1160     1164       +4     

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[zimeg]

🌚 A few thoughts of these changes shared for kind reviewers!

[zimeg]

Suggested change

	var appPath string
	if len(args) > 0 {
	appPath = args[0]
	if _, err := clients.Fs.Stat(appPath); err != nil {
	return slackerror.New(slackerror.ErrNotFound).
	WithMessage("The app path %q could not be found", appPath).
	WithRemediation("Check that the file exists and the path is correct")
	}
	}

🪓 note: I'm curious of removing this in favor of leaving errors to the hook implementations. Removing this might let for strange argument parsing as perhaps:

$ slack run localhost

👾 ramble: For now it seems to make a better experience for the intended filepath arguments I think-

[zimeg]

🗣️ note: IIRC this activity level flag isn't used often so we might encourage examples that outline another common use case?

[zimeg]

📚 note: I'm not so excited about this placeholder but it's clear to me...