🐛 [BUG] - use built-in metric to create Latency SLO On Dynatrace

### SLO Generator Version

v2.3.4

### Python Version

3.10.11

### What happened?

in the documentation, we're shown using the threshold method with an ext: metric from a OneAgent or ActiveGate extension.

```ext:app.request_latency```
is this mandatory, or can we use built-in metrics like those ones ?

``` builtin:service.response.client```
``` builtin:service.keyRequest.response.time ```

it can be great to add a kind of list of metric that we can use in the documentation :)

### What did you expect?

expected to have a valid result using those two builtin metrics
``` builtin:service.response.client```
``` builtin:service.keyRequest.response.time ```

### Screenshots

```bash
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### Relevant log output

_No response_

### Code of Conduct

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