Add documentation for Ruler remote evaluation via Query Frontend

[yeya24]

As a follow up of #6151, we need to add relevant doc to document this option.
How it can be enabled, configuration parameters, pros and cons of the rule evaluation via Query Frontend and Ruler.

[SungJin1212]

@yeya24
Could I take it?
Also, should I change the cortex architecture? I feel like the current architecture is sufficient.

[yeya24]

@SungJin1212 Sure, I will assign to you.

We can leave Cortex architecture unchanged as Ruler evaluate via Query Frontend is just an experimental feature.

[SungJin1212]

@yeya24
Which section is suitable among Operations, Proposals, and Guides? The Proposals or Guide section would be suitable.