sagemaker.model_monitor.Constraints.set_monitoring() method only allows disabling monitoring for string data

**Describe the bug**
I want to override the constraint enforcement for a binary variable. However, the `set_monitoring` method of the sagemaker.model_monitor.Constraints object only allows that to happen for string-type variables with a `string_constraints` section. In addition, the method puts the override inside the `string_constraints` section, contrary to what the official documentation says it should do.

**To reproduce**
- Create a baseline for binary data called `Churn`
- Get the constraints object: `suggested_constraints = baseline_job.suggested_constraints()`
- Set the desired property: `suggested_constraints.set_monitoring(False, feature_name="Churn")`
- Observe the error about the lack of a `string_constraints` section.

**Expected behavior**
The Churn variable's constraints gets a `monitoring_config_overrides` section that includes the value pair `"evaluate_constraints": "Disabled"`.

**Screenshots or logs**
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**System information**
A description of your system. Please provide:
- **SageMaker Python SDK version**: 1.18.51
- **Framework name (eg. PyTorch) or algorithm (eg. KMeans)**:
- **Framework version**: 3.7
- **Python version**: 3.7
- **CPU or GPU**: CPU
- **Custom Docker image (Y/N)**: N

**Additional context**
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