Add myself to project reviewers

Based on https://github.com/kubernetes/community/blob/master/community-membership.md#requirements-1:

The following apply to the part of codebase for which one would be a reviewer in an OWNERS file (for repos using the bot).

> member for at least 3 months

For a couple of years now

> Primary reviewer for at least 5 PRs to the codebase

kubernetes-sigs#285
kubernetes-sigs#275
kubernetes-sigs#267
kubernetes-sigs#254
kubernetes-sigs#181

> Reviewed or merged at least 20 substantial PRs to the codebase

https://github.com/kubernetes-sigs/descheduler/pulls?q=is%3Apr+is%3Aclosed+assignee%3Aingvagabund

> Knowledgeable about the codebase

yes

> Sponsored by a subproject approver
> With no objections from other approvers
> Done through PR to update the OWNERS file

this PR

> May either self-nominate, be nominated by an approver in this subproject, or be nominated by a robot

self-nominating

OWNERS

@@ -9,3 +9,4 @@ reviewers:
 - ravisantoshgudimetla
 - damemi
 - seanmalloy
+- ingvagabund