Add argo-cd to plugin marketplace (#3604)

* Add argo-cd to plugin marketplace

* Correct the Argo CD title

* Add tags to Argo CD plugin description

microsite/data/plugins/argo-cd.yaml

@@ -0,0 +1,12 @@
+---
+title: Argo CD
+author: roadie.io
+authorUrl: https://roadie.io
+category: CI
+description: View Argo CD status for your projects in Backstage.
+documentation: https://roadie.io/backstage/plugins/argo-cd
+iconUrl: https://roadie.io/images/logos/argo.png
+npmPackageName: '@roadiehq/backstage-plugin-argo-cd'
+tags:
+  - cd
+  - ci