feat(ci): configure image build caching

.github/workflows/postgres.yml

@@ -1,6 +1,8 @@
 name: Postgres image
 on:
   push:
+    paths:
+      - postgres/**
     branches:
       - main
     tags:
@@ -39,6 +41,8 @@ jobs:
           build-args: |
             POSTGRES_MAJOR=${{ matrix.postgres_major }}
             POSTGRES_MINOR=${{ fromJSON(env.MINOR_VERSIONS)[matrix.postgres_major] }}
+          cache-from: type=registry,ref=code.icb4dc0.de/prskr/supabase-operator/postgres:buildcache
+          cache-to: type=registry,ref=code.icb4dc0.de/prskr/supabase-operator/postgres:buildcache,mode=max
 
   manifest:
     strategy: