[EPIC] Reformat primitives section

[kaelynj]

As we integrate the directed execution model (executor) into docs, we should reorder how the section on primitives is arranged. The end goal is to have a page ordering like:

└── Execute on QPUs V
    ├── Introduction to primitives (leave page as-is, include brief description of each primitive & when to use which)
    │
    ├── Sampler V
    │   ├── intro/hello world
    │   ├── inputs and outputs
    │   ├── options
    │   ├── e2e examples
    │   ├── BackendSampler → will move to the integrations sections 
    │   └── REST API
    ├── Estimator V
    │   ├── intro/hello world
    │   ├── inputs and outputs
    │   ├── options
    │   ├── e2e examples
    │   ├── BackendSampler → will move to the integrations sections 
    │   └── REST API
    ├──  Executor V
    │  ├── intro/hello world
    │  ├── inputs and outputs
    │  ├── options
    │  ├── e2e examples
    │  ├── BackendSampler → will move to the integrations sections 
    │  └── REST API
    └── Error  mitigation and suppression V
         ├── Error mitigation and suppression techniques
         ├── Noise learning helper
         └── Configure error suppression and mitigation

To keep our sanity and not blow this work up into a single PR, each step is laid out in sub-issues below. The first one (#4614 ) should be completed before starting the rest.

Once that's done, and after the TOC reordering is finalized, we should also move all sections in Introduction to primitives to Qiskit section (save for Primitive details).

[jyu00]

We'll also need content for NoiseLearnerV3

[beckykd]

We'll also need content for NoiseLearnerV3

Also Error mitigation and suppression techniques. And is the plan to merge the intro to options and specify options topics? They're both pretty long.

Should "Configure error suppression and mitigation" be part of each relevant primitive?

[beckykd]

Keep @christopherporter1 in the loop for these.

[jyu00]

fyi The release of Executor will also unblock #4397 (doc on post selection)