Add @rvagg as a FIP editor

[anorth]

I propose @rvagg to be added as as a FIP editor, to increase our numbers a little with an experienced technical expert, especially while we are considering removing editors who have ceased contributing.

@rvagg is already a frequent contributor to FIP discussions and PR review, and I think we can recognize this and gain some more responsiveness on the administrivia by adding him to the crew.

Note to others: we'd still like to add more, especially from outside FilOz. Rod sets a good example of the type of engagement that would encourage us all to want you as a colleague.

Initially proposed in Slack here.

Editors: please leave this PR open for some time after the first two approvals so all current editors have a reasonable chance to comment.

[momack2]

I’m supportive! 👍

[jsoares]

Very supporting, almost a de facto recognition.

[jsoares]

Although not blocking to merging this, we should probably reach a resolution on https://github.com/filecoin-project/FIPs/pull/991/files too, as part of the broader maintenance of the editor list.