SqlServer: add custom convention which adds a blank trigger to all tables

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#27372 changes the SQL Server provider to use OUTPUT without INTO in the update pipeline - this is more efficient, but incompatible with triggers. It also adds a per-table opt-in to allow users to switch to the slower OUTPUT with INTO syntax. This issue tracks adding a custom convention which allows doing that globally.

Depends on:

• Allow applications to create model building conventions (aka public conventions) #214

Split out from #27372

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Removing milestone to discuss whether this belongs in 7.0.