Fix Minio SecurityContext for Mattermost

Fixes the securitycontext for Mattermost's deployment of Minio. See MR: https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/merge_requests/23. This is an issue that the Enterprise Collab team has been running into since the initial MM addon - previous fixes have been poorly tested and didn't work. Tested this fix on RKE2, k3d, and had several others test on RKE2. Also this fix makes sense, since the IB image user is 1001 for minio.

Closes #360 (closed)