Implements #2518 to allow for excluding specific indexes during scaffolding

[jwyza-pi]

Handles #2518. This works around dotnet/efcore#11298.

Example:

Before:

{
  "name": "[dbo].[Widget]",
  "exclude": false
},

 public void Configure(EntityTypeBuilder<Widget> entity)
  {
      entity.ToTable("Widget", tb =>
          {
              tb.HasTrigger("Widget_Insert");
              tb.HasTrigger("Widget_Update");
          });

      entity.HasIndex(e => new { e.CompanyId, e.IsDeleted, e.WidgetName }, "IX_Widget_CompanyIdIsDeletedWidgetName");

      entity.HasIndex(e => e.CompanyId, "UX_Widget_CompanyId_TopLevelWidget")
          .IsUnique()
          .HasFilter("([ParentWidgetId]=(0) AND [IsDeleted]=(0))");
}

After:

{
  "name": "[dbo].[Folder]",
  "exclude": false,
  "excludedIndexes": [
    "UX_Folder_CompanyId_TopLevelFolder"
  ]
},

 public void Configure(EntityTypeBuilder<Widget> entity)
{
    entity.ToTable("Widget", tb =>
        {
            tb.HasTrigger("Widget_Insert");
            tb.HasTrigger("Widget_Update");
        });
  
    entity.HasIndex(e => new { e.CompanyId, e.IsDeleted, e.WidgetName }, "IX_Widget_CompanyIdIsDeletedWidgetName");
}

[ErikEJ]

@jwyza-pi Thanks again for another great contribution - I will get the docs updated