Update docs following 821

[KexyBiscuit]

HasIndex(Expression<Func<TEntity,Object>>) returns IndexBuilder instead of IndexBuilder<TEntity>, so no overload of ForNpgsqlInclude accept Expression<Func<TEntity, object>> now.

This could be merged after targeting a newer version of EFCore, which has the corresponding HasIndex() overload.

[KexyBiscuit]

That was explained in the PR summary, HasIndex returns non-generic IndexBuilder, but the expression-based overload accepts only generic IndexBuilder.

[austindrenski]

That was explained in the PR summary, HasIndex returns non-generic IndexBuilder, but the expression-based overload accepts only generic IndexBuilder.

Right... but #821 is reacting to dotnet/efcore#14641 which generifiesHasIndex(...).

Since our release cadence follows the main EF Core project, the generic HasIndex(...) will be available by the time the documentation is published.

[KexyBiscuit]

I'd like this to be merged after something like #833, since the latest CI version still doesn't support the generic HasIndex.

[roji]

IIRC merging doc changes into dev doesn't make them live in any way - we generate docs from the master branch. So it should be fine to merge this to dev for 3.0 (I'll leave that to @austindrenski).