Replace example matcher from env="production" to env="staging"

- Updated exampleMatcher constant in FilterBar/Views.elm
- Added comment explaining how to change environment
- Rebuilt frontend assets and compressed resources
- Updated asset/assets_vfsdata.go with new frontend build

Signed-off-by: Dmitry Abramov <[email protected]>

Author: demkkka

asset/assets_vfsdata.go

@@ -166,4 +166,4 @@ view { showSilenceButton } { matchers, matcherText, backspacePressed } =
 
 exampleMatcher : String
 exampleMatcher =
-    "env=\"production\""
+    "env=\"staging\""