Docker: Reduce layers in build container and modified initialization of PATH env in final container (#20132)

Multiple local files copied to same destination in one COPY instruction in 0th build container. PATH env variable is modified using the default PATH env variable available in alpine container to achieve the same effect.

Dockerfile

@@ -11,8 +11,7 @@ COPY vendor vendor
 RUN go mod verify
 
 COPY pkg pkg
-COPY build.go build.go
-COPY package.json package.json
+COPY build.go package.json ./
 
 RUN go run build.go build
 
@@ -52,7 +51,7 @@ LABEL maintainer="Grafana team <hello@grafana.com>"
 ARG GF_UID="472"
 ARG GF_GID="472"
 
-ENV PATH=/usr/share/grafana/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin \
+ENV PATH="/usr/share/grafana/bin:$PATH" \
     GF_PATHS_CONFIG="/etc/grafana/grafana.ini" \
     GF_PATHS_DATA="/var/lib/grafana" \
     GF_PATHS_HOME="/usr/share/grafana" \