docs: deploy langfuse for development

docs/langfuse.md

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+# Deploying LangFuse Locally
+
+## Set Up Redis
+
+A local instance of [LangFuse](https://langfuse.com/docs) brings its own Redis instance with some basic authentication setup. If you don't specify the env var `REDIS_AUTH`, the password defaults to `myredissecret` and LangFuse automatically uses the database number `0` of that Redis instance (remember that by default, it comes with 16 databases, 0 to 15).
+If you also run a local instance of Redis for the Companion, you have the following options:
+
+1. Let the Companion use the Redis instance that comes with LangFuse and addressing database `1` by adding these lines in your `config/config.json`:
+
+   ```json
+   "REDIS_PASSWORD": "myredissecret",
+   "REDIS_DB_NUMBER": "1",
+   ```
+
+or
+
+1. Set up your Redis instance directly with the Companion to run on a different port, for example, `6380` (the default port for Redis is `6379`).
+
+   ```shell
+   docker run -d --name redis -p 6380:6379 redis
+   ```
+
+2. Set your `config/config.json` to:
+
+  ```json
+  "REDIS_PORT": "6380",
+  ```
+
+## Deploy LangFuse Locally
+
+1. Clone the LangFuse repository to your local machine:
+
+   ```bash
+   git clone https://github.com/langfuse/langfuse.gitcd langfuse
+   cd langfuse
+   ```
+
+2. Start the application:
+
+   ```bash
+   docker compose up
+   ```
+
+3. Open the web interface:
+
+   ```bash
+   open http://localhost:3000/auth/sign-up
+   ```
+
+4. Create an account, and choose **+ New Organization**. Give your organization a name, and choose **Next**.
+5. On the **Invite Members** page, give your project a name, and choose **Create**.
+6. Go to **API Keys**, and choose **+ Create new API keys**. Copy the `Secret Key`, `Public Key`, and `Host`, and paste them as values into your Kyma Companion's `config/config.json` for, **LANGFUSE_SECRET_KEY**, **LANGFUSE_PUBLIC_KEY**, and **LANGFUSE_HOST**:
+
+  ```json
+  ...
+  "LANGFUSE_HOST": "https://localhost:3000",
+  "LANGFUSE_SECRET_KEY": "<your secret key>",
+  "LANGFUSE_PUBLIC_KEY": "<your public key>",  
+  ```
+
+## Deploy LangFuse on Kubernetes
+
+1. To configure the minimal setup run:
+
+   ```shell
+   kubectl create ns langfuse
+   helm repo add langfuse https://langfuse.github.io/langfuse-k8s
+   helm repo update
+   helm install langfuse langfuse/langfuse --namespace langfuse
+   ```
+
+2. To expose the `langfuse-web` service outside, you need an APIRule. To find out what your `host` is run:
+
+   ```shell
+   kubectl get gateway kyma-gateway -n kyma-system -o=jsonpath='{.spec.servers[0].hosts[0]}'
+   ```
+
+   Now past your `host` into this manifest and apply the APIRule to your cluster.
+
+   ```yaml
+   apiVersion: gateway.kyma-project.io/v1beta1
+   kind: APIRule
+   metadata:
+     labels:
+       app.kubernetes.io/name: langfuse
+     name: langfuse
+     namespace: langfuse
+   spec:
+     gateway: kyma-system/kyma-gateway
+     host: langfuse.<YOUR HOST>
+     rules:
+     - accessStrategies:
+       - handler: no_auth
+       methods:
+       - GET
+       - POST
+       - PUT
+       - OPTIONS
+       path: /.*
+     service:
+       name: langfuse-web
+       port: 3000
+   ```
+
+3. Open the web interface:
+
+   ```bash
+   open http://langfuse.<YOUR HOST>:3000/auth/sign-up
+   ```
+
+4. Create an account, and choose **+ New Organization**. Give your organization a name, and choose **Next**.
+5. On the **Invite Members** page, give your project a name, and choose **Create**.
+6. Go to **API Keys**, and choose **+ Create new API keys**. Copy the `Secret Key`, `Public Key`, and `Host`, and paste them as values into your Kyma Companion's `config/config.json` for, **LANGFUSE_SECRET_KEY**, **LANGFUSE_PUBLIC_KEY**, and **LANGFUSE_HOST**:
+
+   ```json
+   ...
+   "LANGFUSE_HOST": "https://langfuse.<YOUR HOST>:3000",
+   "LANGFUSE_SECRET_KEY": "<your secret key>",
+   "LANGFUSE_PUBLIC_KEY": "<your public key>",  
+   ```