chore: scaffold workspace with nextest and docker compose

Workspace with 6 crates: wfe-core, wfe-sqlite, wfe-postgres,
wfe-opensearch, wfe-valkey, and wfe (umbrella). Nextest profiles
for default, integration, and CI. Docker compose for PostgreSQL,
Valkey, and OpenSearch integration tests.

docker-compose.yml

@@ -0,0 +1,38 @@
+services:
+  postgres:
+    image: postgres:17
+    environment:
+      POSTGRES_USER: wfe
+      POSTGRES_PASSWORD: wfe
+      POSTGRES_DB: wfe_test
+    ports:
+      - "5433:5432"
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U wfe"]
+      interval: 2s
+      timeout: 5s
+      retries: 10
+
+  valkey:
+    image: valkey/valkey:8
+    ports:
+      - "6379:6379"
+    healthcheck:
+      test: ["CMD", "valkey-cli", "ping"]
+      interval: 2s
+      timeout: 5s
+      retries: 10
+
+  opensearch:
+    image: opensearchproject/opensearch:2
+    environment:
+      - discovery.type=single-node
+      - DISABLE_SECURITY_PLUGIN=true
+      - OPENSEARCH_INITIAL_ADMIN_PASSWORD=admin
+    ports:
+      - "9200:9200"
+    healthcheck:
+      test: ["CMD-SHELL", "curl -s http://localhost:9200 | grep -q 'opensearch'"]
+      interval: 5s
+      timeout: 10s
+      retries: 20