chore: add alb ingress controller docs run-it-locally how-to

Author: Kamil Przybyl

docs/ingress-controller.md

@@ -0,0 +1,25 @@
+### Run the ALB Ingress controller locally
+To run the controller on your local machine, ensure you have a valid kubeconfig pointing to the target Kubernetes cluster where the ALB resources should be managed.
+
+##### Environment Variables
+The controller requires specific configuration and credentials to interact with the STACKIT APIs and your network infrastructure. Set the following variables:
+  - STACKIT_SERVICE_ACCOUNT_TOKEN: Your authentication token for performing CRUD operations via the ALB and Certificates SDK.
+  - STACKIT_REGION: The STACKIT region where the infrastructure resides (e.g., eu01).
+  - PROJECT_ID: The unique identifier of your STACKIT project where the ALB will be provisioned.
+  - NETWORK_ID: The ID of the STACKIT network where the ALB will be provisioned.
+```
+export STACKIT_SERVICE_ACCOUNT_TOKEN=<your-token>
+export STACKIT_REGION=<region>
+export PROJECT_ID=<project-id>
+export NETWORK_ID=<network-id>
+```
+Kubernetes Context
+The controller uses the default Kubernetes client. Ensure your KUBECONFIG environment variable is set or your current context is correctly configured:
+```
+export KUBECONFIG=~/.kube/config
+```
+#### Run
+Use the provided Makefile in the root of repository to start the controller:
+```
+make run
+```