Add Artur Khantimirov to the OpenCost Maintainers.

Signed-off-by: Matt Ray <github@mattray.dev>

MAINTAINERS.md

@@ -7,6 +7,7 @@ Official list of [OpenCost Maintainers](https://github.com/orgs/opencost/teams/o
 | Maintainer | GitHub ID | Affiliation | Email |
 | --------------- | --------- | ----------- | ----------- |
 | Ajay Tripathy | @AjayTripathy | Kubecost | <Ajay@kubecost.com> |
+| Artur Khantimirov | @r2k1 | Microsoft | |
 | Matt Bolt | @​mbolt35 | Kubecost | <matt@kubecost.com> |
 | Matt Ray | @mattray | Kubecost | <mattray@kubecost.com> |
 | Michael Dresser | @michaelmdresser | Kubecost | <michael@kubecost.com> |