feat(engine,checker): build extended summary for DB Migration Checker (#395)

Description

Build extended summary for DB Migration Checker:

• make Platform integration optional
• collect session details
• build summary report in Markdown format

Related issue

#395 (closed)

Examples

• https://github.com/postgres-ai/green-zone/pull/8#issuecomment-1237959150
• https://github.com/postgres-ai/green-zone/pull/8#issuecomment-1237970372

Checklist

• MR description has been reviewed
• MR changes are functionally tested
• MR does NOT have text changes OR there are text changes and they have been reviewed
• MR does NOT have API/CLI changes OR there are API/CLI changes and they have been reviewed
• MR does NOT have UI changes OR there are UI changes and they have been reviewed

Closes #395 (closed)