Documentation pointing to non-existent explanation

### Report

Following link (https://github.com/Azure/api-management-self-hosted-gateway/blob/main/helm-charts/azure-api-management-gateway/README.md#:~:text=observability.logs.std.level) is supposed to explain what various logging level means and provide a link for reference where those values are explained. This link does not contain any information about differences between all, debug, info, warn, error or fatal

### Expected Behavior

Documentation shall specify difference what is being logged for each of those values

### Actual Behavior

Going to a page with no explaination

### Steps to Reproduce the Problem

See description

### Logs from self-hosted gateway

See description

### Self-hosted Gateway Version

1.8.1

### Deployment

Self-Managed (YAML/Helm)

### Platform

Microsoft Azure

### Kubernetes Version

1.26

### Anything else?

_No response_