feat: Initial add a component to connect to mysql.

kubernetes/components/connect/mysql/README.md

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+# MySQL Connection Component
+
+This Kustomize component provides a standardized way for applications to connect to the shared MySQL database cluster.
+
+## Features
+
+- Injects standard database connection environment variables.
+- Supports `Deployment`, `StatefulSet`, and `HelmRelease` (standard `bjw-s` app-template structure).
+- Configurable via a local `mysql-secret`.
+
+## Environment Variables
+
+The following variables are injected into the application containers:
+
+| Variable | Source / Value | Description |
+|----------|----------------|-------------|
+| `DB_HOST` | `mysql-innodbcluster-router.database-system.svc.cluster.local` | The internal DNS name for the MySQL router. |
+| `DB_PORT` | `3306` | The default MySQL port. |
+| `DB_USER` | Secret `mysql-secret`, key `DB_USER` | Database username. |
+| `DB_PASSWORD` | Secret `mysql-secret`, key `DB_PASSWORD` | Database password. |
+| `DB_NAME` | Secret `mysql-secret`, key `DB_NAME` | Name of the database. |
+
+## Usage
+
+### 1. Add the component to `kustomization.yaml`
+
+In your application's `kustomization.yaml`, add the component:
+
+```yaml
+components:
+  - ../../components/connect/mysql
+```
+
+### 2. Create the required secret
+
+Ensure a secret named `mysql-secret` exists in the application's namespace with the following keys:
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name: mysql-secret
+stringData:
+  DB_USER: "your-user"
+  DB_PASSWORD: "your-password"
+  DB_NAME: "your-database"
+```
+
+### 3. Overriding defaults
+
+If you need to use a different secret name or override specific variables, you can define them directly in your resource's `env` section. Kustomize will prioritize or merge these depending on the patch type.
+
+For `HelmRelease` using the `bjw-s` template, ensure your controller is named `main` and container is named `main` for the patch to apply automatically.
+
+## Resource Compatibility
+
+- **Deployments**: Targets containers named `app`.
+- **StatefulSets**: Targets containers named `app`.
+- **HelmReleases**: Targets `spec.values.controllers.main.containers.main`.

kubernetes/components/connect/mysql/kustomization.yaml

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+---
+apiVersion: kustomize.config.k8s.io/v1alpha1
+kind: Component
+
+patches:
+  - path: patch-deployment.yaml
+    target:
+      kind: Deployment
+  - path: patch-statefulset.yaml
+    target:
+      kind: StatefulSet
+  - path: patch-helmrelease.yaml
+    target:
+      kind: HelmRelease

kubernetes/components/connect/mysql/patch-deployment.yaml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: placeholder
+spec:
+  template:
+    spec:
+      containers:
+        - name: app
+          env:
+            - name: DB_HOST
+              value: mysql-innodbcluster-router.database-system.svc.cluster.local
+            - name: DB_PORT
+              value: "3306"
+            - name: DB_USER
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_USER
+            - name: DB_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_PASSWORD
+            - name: DB_NAME
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_NAME

kubernetes/components/connect/mysql/patch-helmrelease.yaml

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+apiVersion: helm.toolkit.fluxcd.io/v2
+kind: HelmRelease
+metadata:
+  name: placeholder
+spec:
+  values:
+    controllers:
+      main:
+        containers:
+          main:
+            env:
+              DB_HOST: mysql-innodbcluster-router.database-system.svc.cluster.local
+              DB_PORT: "3306"
+              DB_USER:
+                valueFrom:
+                  secretKeyRef:
+                    name: mysql-secret
+                    key: DB_USER
+              DB_PASSWORD:
+                valueFrom:
+                  secretKeyRef:
+                    name: mysql-secret
+                    key: DB_PASSWORD
+              DB_NAME:
+                valueFrom:
+                  secretKeyRef:
+                    name: mysql-secret
+                    key: DB_NAME

kubernetes/components/connect/mysql/patch-statefulset.yaml

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+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: placeholder
+spec:
+  template:
+    spec:
+      containers:
+        - name: app
+          env:
+            - name: DB_HOST
+              value: mysql-innodbcluster-router.database-system.svc.cluster.local
+            - name: DB_PORT
+              value: "3306"
+            - name: DB_USER
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_USER
+            - name: DB_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_PASSWORD
+            - name: DB_NAME
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_NAME