Update Code of Conduct to the Latest Version of Contributor Covenant

Hi everyone,

I am [Maryblessing Okolie](https://www.linkedin.com/in/maryblessingokolie/), project manager at Contributor Covenant. I see that EnAccess uses [Contributor Covenant v2.1](https://github.com/EnAccess/.github/blob/main/CODE_OF_CONDUCT.md), and I wanted to share a quick update - [Contributor Covenant version 3.0](https://www.contributor-covenant.org/) has now been released, and we would love to see the EnAccess community update to the latest version.

You can learn more about the major changes in this Press Release: https://ethicalsource.dev/blog/contributor-covenant-3/.

If you have any questions, concerns, or need help with the switch, feel free to leave me a comment here.

Thanks!