build(docker): Optimize Docker image layers/caching & bump node to 14.15 (#776)

* refactor(docker): Combine RUN statements to reduce number of image layers

* Add --update && --no-cache to apk add command

* Combine RUN statements in first stage

* Consolidate COPY commands from BUILD_IMAGE

* Add docs & snap to .dockerignore

* Revert first COPY statement in 2nd stage

* Write committag.json in first stage & only do one COPY
Also pin base image Alpine version, and add Docker & GitHub Actions update monitoring via Dependabot

* Bump node to 14.15.4

* Change base image to node:14.15-alpine and remove Dependabot Docker monitoring

* Changes in response to PR comments

* Remove ARG/ENV statements from second build stage

.github/dependabot.yml

@@ -6,3 +6,9 @@ updates:
       interval: daily
       time: '20:00'
     open-pull-requests-limit: 10
+  - package-ecosystem: github-actions
+    directory: '/'
+    schedule:
+      interval: daily
+      time: '20:00'
+    open-pull-requests-limit: 10