Issue-716 - check for duplicate system label

[Fiveofoura]

Create a new warning in studio for duplicate system labels when creating a new field.

Description

The same system label could potentially be used for more than one field. When creating a new field with a used system label, the new display label overwrites the old one, changing the display label for both fields.
A warning now appears on the form if the system label already exists in the module when attempting to create a new field. The field will not be created in this scenario.
Issue here: #716

Motivation and Context

Two fields had the same system label. One field's display label was changed to the newly create one as a result.

How To Test This

See #716

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.

[SuiteBot]

All committers have signed the CLA.