otelconf: add support for `log_level`

### Component

Config

### Problem Statement

As per suggestion in https://github.com/open-telemetry/opentelemetry-go-contrib/pull/8026#discussion_r2548363259

### Proposed Solution

Use the `LogLevel` field and call `SetLogger` with the appropriate level

### Alternatives

_No response_

### Prior Art

_No response_

### Additional Context

_No response_