Set up the page nesting and separate content into`Sampler` and `Estimator` sections

[kaelynj]

Move/separate out the following pages into a Sampler Estimator and Executor section in the TOC

• Get started with primitives
• Primitive inputs and outputs
• Primitives examples
• Primitives with REST API
• Introduction to options (also merge with Specify options)

Final section ordering should look like:

    ├── Introduction V
    │   ├── What is a primitive?
    │   ├── Why did Qiskit introduce primitives?
    │   ├── Brief description of each primitive & when to use which
    │   └── Configure error suppression and mitigation
    ├── 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

[kaelynj]

Closed by #4640