Add issue_type support for REST API

What does this MR do?

Related issue: #260375 (closed)

Pre-req MR: !60173 (merged)

Summary: Adds ability to read/create/edit/filter issues based on issue_type param in external REST API.

Changes in this MR:

• Expose issue_type in issue entity
• Accept issue_type for POST/PUT requests
• Accept issue_type for GET /issues request
• Ensure references to PUT/DELETE operations are named consistently in specs & docs

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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