Each tenant can configure lookback-delta separately

[shichanglin5]

The monitoring data of different tenants is isolated, and the sampling interval of these tenants may be different (some 60 seconds, some 15s, or even 5s). Currently, the lookback-delta can only be configured through engine.Config, which cannot adapt to all tenant monitoring queries;

I suggest that this parameter can be put into runtime config to support different tenants to configure different lookback-delta parameters.

[shichanglin5]

I see that some people in issuse have also put forward the need to use lookback-delta parameter values different from those in engine.config, by adding lookback-delta parameters. I think it will be better to put it in runtime config and will have better compatibility.