Speed up docker image build by use layer cache (#4038)

* speed up docker image build by use layer cache

* rearrenge Dockerfile

* enable docker layer cache in github action

.github/workflows/ci.yml

@@ -76,4 +76,11 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - run: git submodule update --init --recursive --force
+
+      # In this step, this action saves a list of existing images,
+      # the cache is created without them in the post run.
+      # It also restores the cache if it exists.
+      - uses: satackey/[email protected]
+        continue-on-error: false
+
       - run: docker build .

Dockerfile

@@ -4,6 +4,13 @@ FROM docker.io/library/golang:1.18-alpine3.15 AS builder
 RUN apk --no-cache add make gcc g++ linux-headers git bash ca-certificates libgcc libstdc++
 
 WORKDIR /app
+
+# Get dependencies - will also be cached if we won't change go.mod/go.sum
+COPY go.mod .
+COPY go.sum .
+RUN go mod download
+
+
 ADD . .
 
 RUN make erigon rpcdaemon integration sentry txpool downloader hack observer db-tools