CI: sign plugin during release (#1039)

* Add grafana toolkit package

* CI: skip adding binaries to release branch

* CI: test signing plugin

* CI: skip branch build for test releases

* CI: do not use ssh key for fetching

* CI: get plugin in a separate image to avoid git LFS error

* CI: fix attaching workspace

* CI: fix attaching dir

* CI: adjust release process

* CI: clean up

.gitignore

@@ -31,6 +31,10 @@ yarn-error.log
 
 # Built plugin
 dist/
+ci/
+
+# Grafana toolkit configs
+.prettierrc.js
 
 # locally required config files
 public/css/*.min.css