Update project Code of Conduct to match WordPress Project

[dd32]

Description

This PR updates the repository to use the WordPress project's Code of Conduct rather than maintaining a project-specific one:

• Removes the local CODE_OF_CONDUCT.md, which predates the WordPress Coding Standards being part of the WordPress project.
• Adds a link from the README pointing contributors to the WordPress project Code of Conduct.

Suggested changelog entry

None required.

Related issues/external references

Related: #2722 (comment)
Partially supersedes #2724

[GaryJones]

I checked the diff between the COC we had in the project, and the WP project one that this PR references. I think it makes sense to centralise and align on contributor expectations between WordPressCS and other repos under the WordPress banner.

[jrfnl]

I'm okay with this.

The fact that WPCS had its own code of conduct was a historic artifact of the WordPress project not having one and WPCS identifying the need for one.

Now WP has a CoC, I'm happy to defer to the WP one.

FYI: We normally merge with two maintainer approvals - I'm going to leave this PR open for a few more days to allow the remaining two maintainers to pitch in though, in case they would have different views.

[rodrigoprimo]

I also agree with this change.

The only concern I have is that https://github.com/WordPress/WordPress-Coding-Standards/blob/develop/.github/CONTRIBUTING.md?plain=1#L32 points to the deleted WPCS CoC, and will have a broken link if this PR is merged as is. I would suggest updating the link to point to the WordPress Project CoC as a defensive change, so this PR is independent of #2735, but I'm open to other approaches as well.

[jrfnl]

@dd32 Seeing four ++three++ approvals, would you mind actioning @rodrigoprimo's comment ? Once that's done, we'll get this merged ASAP.