Adding flat file import service and related contracts

[aasimkhan30]

Description

1. Enabled parallel processing and made apis parallel safe
2. Relying on connection service to get connection string. Frontend now just gives owner uri and database name for the connection.
3. Removing Entra token passing to Bcp Process. Instead we are going to rely on auth provider to get tokens.

Code Changes Checklist

• New or updated unit tests added
• All existing tests pass (dotnet test)
• Code follows contributing guidelines
• Logging/telemetry updated if relevant
• No protocol or behavioral regressions

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[github-actions]

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