improve error message for func run making it more beginner friendly

[RayyanSeliya]

Changes

• 🧹 Update error message shown when func run is run outside a function directory.
• Made the message more user-friendly and easier for beginners to understand.
• Added step-by-step workflow guidance with examples for both new and existing functions.
• Provides context-specific guidance that func run runs functions locally for testing.

/kind enhancement

Fixes #3021

Release Note

Improve error message when `func run` is run outside function directory
to be more beginner-friendly, include step-by-step workflow guidance, and 
explain that func run is used for local testing.

[knative-prow]

Hi @RayyanSeliya. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.41%. Comparing base (ec7ff7e) to head (4c37de9).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/run.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3022      +/-   ##
==========================================
+ Coverage   57.67%   59.41%   +1.74%     
==========================================
  Files         133      133              
  Lines       17030    17030              
==========================================
+ Hits         9822    10119     +297     
+ Misses       6305     5952     -353     
- Partials      903      959      +56     

Flag	Coverage Δ
e2e-tests	40.76% <0.00%> (+7.58%)	⬆️
integration-tests	54.08% <0.00%> (+1.61%)	⬆️
unit-tests	46.33% <0.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[lkingland]

/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lkingland, RayyanSeliya

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [lkingland]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment