Update CODEOWNERS entry for release note docs files

[colleenmcginnis]

@pierrehilbert @ebeahan how do you feel about co-owning the release notes docs files to remove friction when approving/merging backports and forwardports on release day (like this one and this one)? If the initial PR was approved by the docs team and the doc preview builds successfully, you should be able to merge backports/forwardports.

cc @karenzone

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[pierrehilbert]

I prefer not doing that otherwise folks from my team will get pinged for those PR and it will create unnecessary noise.
Another option would be to create a new team: elastic-agent-leads to add it there but not sure this is something we really need.
Also, Eric and I have permissions to force merge so in the worse case, we don't need you to re-approve things to be able to merge them.