Build for arm64 on arm64 runner. Parallelize arm64, x64 docker builds

- Building arm64 image on an ubuntu arm64 runner reduces `yarn build'
  step time by 75% from 12mins to 3mins.
  - This is because no QEMU emulation for arm64 on x86 is required now
- Parallelizing x64 and arm64 platform builds halves build time on top
  - Revert to use standard ubuntu-latest runner as large x64 runner
    doesn't give much more speed improvements

This results an effective additional 50%-66% reduction in build time
on top of #987.

So a full dockerize workflow run now takes *10 mins* vs previous 35+mins.
This is a total of *72% improvement* in max dockerize run time.

Get additional speed improvements when docker layer cache hit.

.github/workflows/dockerize.yml

@@ -38,13 +38,16 @@ env:
 jobs:
   build:
     name: Publish Khoj Docker Images
-    runs-on: ubuntu-linux-x64-high
     strategy:
       fail-fast: false
       matrix:
         image:
           - 'local'
           - 'cloud'
+        platform:
+          - linux/amd64
+          - linux/arm64
+    runs-on: ${{ matrix.platform == 'linux/arm64' && 'ubuntu-linux-arm64' || 'ubuntu-latest' }}
     steps:
       - name: Checkout Code
         uses: actions/checkout@v3
@@ -78,7 +81,7 @@ jobs:
         with:
           context: .
           file: Dockerfile
-          platforms: linux/amd64, linux/arm64
+          platforms: ${{ matrix.platform }}
           push: true
           tags: |
             ghcr.io/${{ github.repository }}:${{ env.DOCKER_IMAGE_TAG }}
@@ -86,8 +89,8 @@ jobs:
           build-args: |
             VERSION=${{ steps.hatch.outputs.version }}
             PORT=42110
-          cache-from: type=gha,scope=${{ matrix.image }}
+          cache-from: type=gha,scope=${{ matrix.image }}-${{ matrix.platform }}
-          cache-to: type=gha,mode=max,scope=${{ matrix.image }}
+          cache-to: type=gha,mode=max,scope=${{ matrix.image }}-${{ matrix.platform}}
 
       - name: 📦️⛅️ Build and Push Cloud Docker Image
         uses: docker/build-push-action@v4
@@ -95,7 +98,7 @@ jobs:
         with:
           context: .
           file: prod.Dockerfile
-          platforms: linux/amd64, linux/arm64
+          platforms: ${{ matrix.platform }}
           push: true
           tags: |
             ghcr.io/${{ github.repository }}-cloud:${{ env.DOCKER_IMAGE_TAG }}
@@ -103,5 +106,5 @@ jobs:
           build-args: |
             VERSION=${{ steps.hatch.outputs.version }}
             PORT=42110
-          cache-from: type=gha,scope=${{ matrix.image }}
+          cache-from: type=gha,scope=${{ matrix.image }}-${{ matrix.platform }}
-          cache-to: type=gha,mode=max,scope=${{ matrix.image }}
+          cache-to: type=gha,mode=max,scope=${{ matrix.image }}-${{ matrix.platform}}