RFR: Add missing JFR mailinglist [v2]

[Jesper Wilhelmsson]

On Thu, 4 Feb 2021 11:23:06 GMT, Yang Yi <github.com+5010047+kelthuzadx at openjdk.org> wrote:

>> Hi, I found that the code owner section of the latest version is missing jfr-related content, this PR will amend this content.
>
> Yang Yi has updated the pull request incrementally with one additional commit since the last revision:
> 
>   just reserve JFR

Marked as reviewed by jwilhelm (Lead).

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PR: https://git.openjdk.java.net/guide/pull/44