Add support for update cmd in the hooks

[haijianyang]

In multi tenant SasS system, I want to update cmd before process.

type RedisHooks struct {} func (h *RedisHooks) BeforeProcess(ctx context.Context, cmd redis.Cmder) (context.Context, error) { tenantID, ok := ctx.Value(TenantKey{}).(string) if !ok { return ctx, nil	} // Update cmd there. // For example: when use redis.set, could set newKey = tenantID + oldKey return ctx, nil }

[qiangwang-uestc]

meet same question