Provide errorgroup instead of waitgroup as alternative for concurrent activity execution

[DerkSchooltink]

I can do something like this:

wg := workflow.NewWaitGroup()
wg.Add(2)

var wgErr error
workflow.Go(ctx, func(ctx workflow.Context) {
    defer wg.Done()
    if _, err := workflow.ExecuteActivity[any](ctx, workflow.DefaultActivityOptions, func, ...).Get(ctx); err != nil {
        wgErr = err
    }
})

workflow.Go(ctx, func(ctx workflow.Context) {
    defer wg.Done()
    if _, err := workflow.ExecuteActivity[any](ctx, workflow.DefaultActivityOptions, func, ...).Get(ctx); err != nil {
        wgErr = err
    }
})

wg.Wait(ctx)
if wgErr != nil {
    return wgErr
}

But capturing an error can be simplified by using the concept of an error group: https://pkg.go.dev/golang.org/x/sync/errgroup

It would look like this:

gctx, g := workflow.WithErrGroup(ctx)
g.Go(func(ctx workflow.Context) error {
	if _, err := workflow.ExecuteActivity[any](ctx, workflow.DefaultActivityOptions, func, ...).Get(ctx); err != nil {
		return err
	}
	return nil
})

g.Go(func(ctx workflow.Context) error {
	if _, err := workflow.ExecuteActivity[any](ctx, workflow.DefaultActivityOptions, func, ...).Get(ctx); err != nil {
		return err
	}
	return nil
})

if err := g.Wait(gctx); err != nil {
	return err
}

I can open up a PR for this to show you how it looks like. It is functionally close to the impl. of the waitgroup.