Fix to #26676 - EF Core 6 - IsTemporal adds an unnecessary migration when DefaultSchema is configured at the DbContext Level

[maumar]

Problem was a discrepancy between RelationalModel build in runtime and the current model (from OnModelCreating) - relational model would set history table schema annotation using the table schema or default schema, however current model wouldn't set those annotations.
Model differ would then pick up on those differences and create migration to set the schema for history table. When building actual migration sql we already compensated for the difference and not generate actual sql code, but the problem persists.

Fix is to improve the temporal convention so that history table schema in current model (more) closely resembles the temporal table schema and therefore is similar to RelationalModel generated in runtime.

Fixes #26676

[AndriySvyryd]

I assume that the issue is that migration snapshot doesn't contain the history schema annotation because it's the default. In cases like these we keep the default logic in the extensions, but add a redundant annotation using a convention, see SqlServerValueGenerationStrategyConvention

This allows the model to be more functional if the convention is removed and potentially can be improved upon when #9329 is implemented.