Uniform ed25519 usage across SSH docs

[jezhou8]

Why: I was trying to add a new ssh key and noticed that github now accepts the more secure ed25519 encryption standard! However, in the documentation, some parts of the tutorial still used referenced the old RSA steps. So I wanted to help make the documentation more uniform and use ed25519.

What's being changed:

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging.
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[nschonni]

Seems like there are a few competing PRs for this #1074 and #1063, I guess we'll see which lands first 😄

[github-actions]

This PR is stale because it has been open 7 days with no activity and will be automatically closed in 3 days. To keep this PR open, update the PR by adding a comment or pushing a commit.

[janiceilene]

I missed this one, sorry about that @jezhou8! I'll get this triaged for review ✨

[shati-patel]

Hello @jezhou8! Thank you for proposing a pull request for fixing this problem. We're really grateful for the help we've been receiving from the community 💟

Your fix was totally right, but we had a slightly earlier pull request (#1074) that fixed the same issue, so I'm going to close this pull request ✔️ Thank you again for contributing 😊