[Cosmos] Fix mismatching type of ConsistencyPolicy with docstring

[allenkim0129]

Description

Tackling the bullet point items related to ConsistencyPolicy type hint for GA release: #43211

The typehint for ConsistencyPolicy in docstring and actual code were mismatching. This fix will sync the typehints for them.

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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[Copilot]

Pull Request Overview

This PR fixes a type annotation mismatch for the ConsistencyPolicy attribute in the DatabaseAccount class. The docstring type hint and actual code implementation had inconsistent type annotations.

• Updates docstring type annotation from Dict[str, Union[str, int]] to dict[str, str]
• Updates instance variable type annotation from Optional[UserConsistencyPolicy] to Optional[dict[str, str]]

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

azure-cosmos

[tvaron3]

LGTM