fix: use timestamp with time zone in PostgreSQL

[yi-Xu-0100]

Describe the change

Use timestamp with time zone in postgresql.

Describe your implementation or design

Only add column type.

Additional context

Relative issue: #1373

[Copilot]

Pull Request Overview

This PR updates the PostgreSQL persistence provider to use timestamp with time zone instead of timestamp without time zone for all DateTime columns. This change ensures proper timezone handling for workflow-related timestamps.

Key changes:

• Modified entity configurations to specify timezone-aware timestamp columns
• Updated the EF Core model snapshot to reflect the new column types
• Added a database migration to alter existing timestamp columns

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
PostgresContext.cs	Added OnModelCreating override to configure DateTime properties with timezone-aware column types
PostgresPersistenceProviderModelSnapshot.cs	Updated model snapshot to reflect new timestamp column types and EF Core version upgrade
20250807084543_ChangeDataTimeTypeForPostgreSQL.cs	Migration file to alter existing DateTime columns from timezone-naive to timezone-aware

Files not reviewed (1)

• src/providers/WorkflowCore.Persistence.PostgreSQL/Migrations/20250807084543_ChangeDataTimeTypeForPostgreSQL.Designer.cs: Language not supported