chore(apps): move icons into the apps folder (#3139)

* chore(apps): move icons into the apps folder

* rename to `icon.png`

* replace solr image

* remove `docs/` from gitignore

* move app specific docs into app folder [skip ci]

* fix some links

* chore(apps): update image links temporary

charts/stable/onlyoffice-document-server/Chart.yaml

@@ -17,7 +17,7 @@ description: 'ONLYOFFICE Document Server is an online office suite comprising vi
   Open XML formats: .docx, .xlsx, .pptx and enabling collaborative editing in real
   time.'
 home: https://github.com/truecharts/apps/tree/master/charts/stable/onlyoffice-document-server
-icon: https://truecharts.org/_static/img/appicons/onlyoffice-document-server.png
+icon: https://truecharts.org/img/appicons/onlyoffice-document-server.png
 keywords:
 - onlyoffice
 kubeVersion: '>=1.16.0-0'