[feature] add ferretdb tests (#1464)

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## What this PR does


### Release note

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```release-note
[feature] add ferretdb tests
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- Tests
- Added an end-to-end test that provisions a FerretDB instance on
Kubernetes, waits for readiness and init completion, verifies
connectivity to read/write Postgres services (including endpoint
convergence), accounts for known RO delays, and performs full cleanup.
Uses timeouts and retries for stability.
- Chores
  - No user-facing product changes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

hack/e2e-apps/ferretdb.bats

@@ -0,0 +1,46 @@
+#!/usr/bin/env bats
+
+@test "Create DB FerretDB" {
+  name='test'
+  kubectl apply -f - <<EOF
+apiVersion: apps.cozystack.io/v1alpha1
+kind: FerretDB
+metadata:
+  name: $name
+  namespace: tenant-test
+spec:
+  backup:
+    destinationPath: "s3://bucket/path/to/folder/"
+    enabled: false
+    endpointURL: "http://minio-gateway-service:9000"
+    retentionPolicy: "30d"
+    s3AccessKey: "<your-access-key>"
+    s3SecretKey: "<your-secret-key>"
+    schedule: "0 2 * * * *"
+  bootstrap:
+    enabled: false
+  external: false
+  quorum:
+    maxSyncReplicas: 0
+    minSyncReplicas: 0
+  replicas: 2
+  resources: {}
+  resourcesPreset: "micro"
+  size: "10Gi"
+  users:
+    testuser:
+      password: xai7Wepo
+EOF
+  sleep 5
+  kubectl -n tenant-test wait hr ferretdb-$name --timeout=100s --for=condition=ready
+  kubectl -n tenant-test wait job.batch postgres-$name-init-job --timeout=50s --for=condition=Complete
+  timeout 40 sh -ec "until kubectl -n tenant-test get svc ferretdb-$name-postgres-r -o jsonpath='{.spec.ports[0].port}' | grep -q '5432'; do sleep 10; done"
+  timeout 40 sh -ec "until kubectl -n tenant-test get svc ferretdb-$name-postgres-ro -o jsonpath='{.spec.ports[0].port}' | grep -q '5432'; do sleep 10; done"
+  timeout 40 sh -ec "until kubectl -n tenant-test get svc ferretdb-$name-postgres-rw -o jsonpath='{.spec.ports[0].port}' | grep -q '5432'; do sleep 10; done"
+  timeout 120 sh -ec "until kubectl -n tenant-test get endpoints ferretdb-$name-postgres-r -o jsonpath='{.subsets[*].addresses[*].ip}' | grep -q '[0-9]'; do sleep 10; done"
+  # for some reason it takes longer for the read-only endpoint to be ready
+  #timeout 120 sh -ec "until kubectl -n tenant-test get endpoints ferretdb-$name-postgres-ro -o jsonpath='{.subsets[*].addresses[*].ip}' | grep -q '[0-9]'; do sleep 10; done"
+  timeout 120 sh -ec "until kubectl -n tenant-test get endpoints ferretdb-$name-postgres-rw -o jsonpath='{.subsets[*].addresses[*].ip}' | grep -q '[0-9]'; do sleep 10; done"
+  kubectl -n tenant-test delete ferretdb.apps.cozystack.io $name
+  kubectl -n tenant-test delete job.batch/postgres-$name-init-job
+}