Setup DCO workflow

[Warashi]

What this PR does / why we need it:

This PR adds a workflow to check DCO.
I added this workflow because the app to check DCO is now down.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[t-kikuc]

Thanks!
dcoapp/app#211 (comment) is related.

After the DCO recovers, this action will be removed, right? @Warashi @khanhtc1202

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.38%. Comparing base (a949b4f) to head (2b96b79).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4944      +/-   ##
==========================================
- Coverage   29.39%   29.38%   -0.02%     
==========================================
  Files         322      322              
  Lines       40852    40852              
==========================================
- Hits        12010    12004       -6     
- Misses      27882    27888       +6     
  Partials      960      960              

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[Warashi]

After the DCO recovers, this action will be removed, right? @Warashi @khanhtc1202

I think so.
I noticed some actions in this workflow is not allowed in this repository, so I'll push some fix.

[t-kikuc]

Thank you so much, I commented a nit.

[t-kikuc]

[IMO] How about specifying this DCO is a workaround?

Suggested change

	name: DCO
	name: DCO-workaround

[Warashi]

This workflow runs as this.
https://github.com/pipe-cd/pipecd/actions/runs/9377057788/job/25817994492?pr=4944

@khanhtc1202 Since I cannot modify branch protection rules, please change the required checks.

[khanhtc1202]

@Warashi Updated the branch protection rules to remove DCO workflow as required step 👍

[khanhtc1202]

Thank you 👍

[ffjlabo]

Thanks!

[Warashi]

@khanhtc1202
I merged this PR, so please update the branch protection rules to add DCO-workaround as required.