Add `deprecated` property for GraphQL

What does this MR do?

Add support for a new deprecated property for GraphQL BaseField.

This property sets the deprecation_reason property with the added semantics of the milestone that the deprecation happened in.

Also adding a new section to the GraphQL Styleguide on how to deprecate fields.

Issue: #199952 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done