added instructions to docs for adding custom user roles

[ricklarsen]

What does this PR do?

adds instructions for add new user roles into users.properties

Who is reviewing it?

@shaundmorris @clockard @sgalla @rececoffin @jaymcnallie @zach3904

Select relevant component teams:

@codice/docs

How should this be tested?

review content for clarity and accuracy

Checklist:

• [x] Documentation Updated
• [ ] Update / Add Threat Dragon models
• [ ] Update / Add Unit Tests
• [ ] Update / Add Integration Tests

Notes on Review Process

Please see Notes on Review Process for further guidance on requirements for merging and abbreviated reviews.

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• ❓ (Question Mark) This comment is to gain a clearer understanding of design or code choices, clarification is required but action may not be necessary for approval.
• ❗ (Exclamation Mark) This comment is critical and requires clarification or action before approval.

[ricklarsen]

build now

[cxddfbot]

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[cxddfbot]

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[ricklarsen]

build now

[cxddfbot]

Internal build has been started, your results will be available at build completion.

[cxddfbot]

Build SUCCESS See the job results in legacy Jenkins UI or in Blue Ocean UI.