feat: add PushSecret generator design (external-secrets#2665)

Signed-off-by: Moritz Johner <[email protected]>

design/009-pushsecret-generator.md

@@ -0,0 +1,62 @@
+```yaml
+---
+title: PushSecret generator integration
+version: v1alpha1
+authors: Moritz Johner
+creation-date: 2023-08-25
+status: draft
+---
+```
+
+# PushSecret Generator integration
+
+## Table of Contents
+
+<!-- toc -->
+// autogen please
+<!-- /toc -->
+
+## Summary
+
+This design document describes how `PushSecret` can leverage generators to generate short-lived credentials without the need of an intermediary `Secret` resource.
+
+## Motivation
+
+Currently, the process of using secure passwords and short-lived credentials within the External Secrets Operator involves multiple steps.
+Users need to create an `ExternalSecret` resource to generate a value which is stored in a `Secret` resource. This Secret resource is then pushed to a provider using a `PushSecret` resource. However, this intermediary step adds unnecessary complexity and inconvenience to the workflow.
+
+## Proposal
+
+To simplify the workflow and enhance user experience, the proposal is to integrate generators directly into the `PushSecret` resource. This will allow users to specify a generator using a `generatorRef` within the PushSecret manifest. When the PushSecret reconciliation process occurs, a value will be generated using the specified generator. This generated value will be securely pushed to the provider and stored there.
+
+```yaml
+apiVersion: external-secrets.io/v1alpha1
+kind: PushSecret
+spec:
+  selector:
+    generatorRef:
+      apiVersion: generators.external-secrets.io/v1alpha1
+      kind: Password
+      name: "my-password"
+```
+
+## Consequences
+
+* **Simplified Workflow**: This change will simplify the process of generating and pushing secrets by eliminating the need for an intermediary Secret resource.
+
+* **Enhanced Security**: As secrets are generated and pushed directly, there will be a reduction in potential vulnerabilities that may arise from the management of intermediary resources.
+
+* **Increased Flexibility**: Integrating generators into PushSecrets allows for more customization and flexibility in generating secrets according to specific requirements.
+
+* **Potential Learning Curve**: Users who are accustomed to the previous workflow may need to adapt to the new approach, which could require some learning and adjustment.
+
+* **API and Documentation Update**: The API changes need to be well-documented to ensure users understand how to utilize the new feature effectively.
+
+
+## Acceptance Criteria
+
+* tests: controller tests for this new field should be sufficient
+* the API changes need to be documented
+    * API/CRD spec inline documentation
+    * PushSecret API documentation
+    * Guides section for `PushSecret` + `generator` functionality