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/esphome/Chart.yaml

@@ -8,7 +8,7 @@ deprecated: false
 description: ESPHome is a system to control your ESP8266/ESP32 by simple yet powerful
   configuration files and control them remotely through Home Automation systems.
 home: https://github.com/truecharts/apps/tree/master/charts/stable/esphome
-icon: https://truecharts.org/_static/img/appicons/esphome.png
+icon: https://truecharts.org/img/appicons/esphome.png
 keywords:
 - esphome
 kubeVersion: '>=1.16.0-0'