Add docker syntax and re-add cache-from

[skip ci]

Author: S7evinK

.github/workflows/docker.yml

@@ -137,6 +137,7 @@ jobs:
         id: docker_build_demo_pinecone
         uses: docker/build-push-action@v3
         with:
+          cache-from: type=registry,ref=ghcr.io/${{ env.GHCR_NAMESPACE }}/dendrite:buildcache
           context: .
           file: ./build/docker/Dockerfile.demo-pinecone
           platforms: ${{ env.PLATFORMS }}
@@ -150,6 +151,7 @@ jobs:
         id: docker_build_demo_pinecone_release
         uses: docker/build-push-action@v3
         with:
+          cache-from: type=registry,ref=ghcr.io/${{ env.GHCR_NAMESPACE }}/dendrite:buildcache
           context: .
           file: ./build/docker/Dockerfile.demo-pinecone
           platforms: ${{ env.PLATFORMS }}
@@ -195,6 +197,7 @@ jobs:
         id: docker_build_demo_yggdrasil
         uses: docker/build-push-action@v3
         with:
+          cache-from: type=registry,ref=ghcr.io/${{ env.GHCR_NAMESPACE }}/dendrite:buildcache
           context: .
           file: ./build/docker/Dockerfile.demo-yggdrasil
           platforms: ${{ env.PLATFORMS }}
@@ -208,6 +211,7 @@ jobs:
         id: docker_build_demo_yggdrasil_release
         uses: docker/build-push-action@v3
         with:
+          cache-from: type=registry,ref=ghcr.io/${{ env.GHCR_NAMESPACE }}/dendrite:buildcache
           context: .
           file: ./build/docker/Dockerfile.demo-yggdrasil
           platforms: ${{ env.PLATFORMS }}

build/docker/Dockerfile.demo-pinecone

@@ -1,3 +1,5 @@
+#syntax=docker/dockerfile:1.2
+
 FROM --platform=${BUILDPLATFORM} ghcr.io/element-hq/dendrite:buildcache AS build
 
 FROM alpine:latest

build/docker/Dockerfile.demo-yggdrasil

@@ -1,3 +1,5 @@
+#syntax=docker/dockerfile:1.2
+
 FROM --platform=${BUILDPLATFORM} ghcr.io/element-hq/dendrite:buildcache AS build
 
 FROM alpine:latest