chore: update reference in preparation for image publish (#133)

## Description

Fixes the image reference in preparation for publishing the plugin
image.

## Related Issue

Relates to defenseunicorns/uds-common#209

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [X] Other (security config, docs update, etc)

## Checklist before merging

- [X] Test, docs, adr added or updated as needed
- [X] [Contributor Guide
Steps](https://github.com/defenseunicorns/uds-package-mattermost/blob/main/CONTRIBUTING.md#developer-workflow)
followed

bundle/uds-bundle.yaml

@@ -75,7 +75,7 @@ packages:
             - path: "mattermostApp.extraInitContainers"
               value:
                 - name: mattermost-extra-plugins
-                  image: uds-package-mattermost/mattermost-extra-plugins:latest
+                  image: ghcr.io/defenseunicorns/uds-package-mattermost/mattermost-plugins:latest
                   imagePullPolicy: Always
                   volumeMounts:
                     - name: mattermost-plugins

plugins/zarf.yaml

@@ -11,9 +11,9 @@ components:
   - name: mattermost-plugins
     required: true
     images:
-      - uds-package-mattermost/mattermost-extra-plugins:latest
+      - ghcr.io/defenseunicorns/uds-package-mattermost/mattermost-plugins:latest
     actions:
       onCreate:
         before:
           - cmd: |
-              docker buildx build --load . -t uds-package-mattermost/mattermost-extra-plugins:latest --platform linux/###ZARF_PKG_ARCH###
+              docker buildx build --load . -t ghcr.io/defenseunicorns/uds-package-mattermost/mattermost-plugins:latest --platform linux/###ZARF_PKG_ARCH###