[DXCDT-157] Add datadog_region validation

[sergiught]

Description

Fixes: #145.

We are adding datadog_region validation in this one to help with understanding the cryptic error message we get when the region is wrong. Within our API we only accept the following case sensitive options:

      datadogRegion: {
        type: 'string',
        description: 'Datadog region',
        enum: ['us', 'eu', 'us3', 'us5'],
      },

Checklist

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Auth0 Code of Conduct

• I have read and agreed to the terms within the Auth0 Code of Conduct

Auth0 General Contribution Guidelines

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Changes include test coverage?

• Yes
• Not needed

Does the description provide the correct amount of context?

• Yes, the description provides enough context for the reviewer to understand what these changes accomplish

Have you updated the documentation?

• Yes, I've updated the appropriate docs
• Not needed

Is this code ready for production?

• Yes, all code changes are intentional and no debugging calls are left over