add DefaultContext for slog

[lingdor]

I have some package in my project like: gorm , gin, slog. I don't want dependant on gorm and gin, How can i use traceid linked log content between gorm and gin module?

I want:

package gin

func Request1(){

logger :=slog.With("traceid",123)
ctx:=context.Background()
ctx=slog.NewContext(ctx,logger)
gorm.ReadDB(ctx)
}

package  gorm

func ReadDB(ctx context.Context){
     logger:=slog.DefaultContext(ctx)
    logger.Info("db is ready")
}

so, all modules can write one attribute in one context , and don't need rewrite slog handle.

thanks

my proposal golang/go#66168

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