migrate files from `qiskit` to `Qiskit/docs` and convert `.rst` files to `.mdx`

[javabster]

The following pages currently live in https://github.com/Qiskit/qiskit/tree/main/docs and and https://github.com/Qiskit/qiskit-tutorials/tree/master/tutorials. They should be moved to this repo and stored in either the start, build, test, run or optimize folders.

Important: Files in .ipynb format should be migrated over without changes, maintaining the git history. Files in .rst format should first be moved over in their existing format (with git history maintained) and then converted to .mdx once the file has been moved here

### Files to migrate to docs/start
- [ ] Migration Guides - https://github.com/Qiskit/qiskit/blob/main/docs/migration_guides/algorithms_migration.rst (convert to `.mdx`)
- [ ] Migration Guides - https://github.com/Qiskit/qiskit/blob/main/docs/migration_guides/opflow_migration.rst (convert to `.mdx`)
- [ ] Migration Guides - https://github.com/Qiskit/qiskit/blob/main/docs/migration_guides/qi_migration.rst (convert to `.mdx`)

### Files to migrate to docs/build
- [ ] Build Circuits with Qiskit - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits/01_circuit_basics.ipynb
- [ ] Build Circuits with Qiskit - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits/1_getting_started_with_qiskit.ipynb
- [ ] Build Circuits with Qiskit - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits/2_plotting_data_in_qiskit.ipynb
- [ ] Build Circuits with Qiskit - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/01_advanced_circuits.ipynb
- [ ] Build Circuits with Qiskit - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/02_operators_overview.ipynb
- [ ] Build Circuits with Qiskit - https://github.com/Qiskit/qiskit/blob/main/docs/explanation/endianness.rst (convert to `.mdx`)
- [ ] Advanced circuit options / Pulse - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/05_pulse_gates.ipynb
- [ ] Advanced circuit options / Pulse - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/06_building_pulse_schedules.ipynb
- [ ] Advanced circuit options / Pulse - https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/07_pulse_scheduler.ipynb

### Files to migrate to docs/transpile
- [ ] https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/04_transpiler_passes_and_passmanager.ipynb

### Files to migrate to docs/test
- [ ] https://github.com/Qiskit/qiskit/blob/main/docs/how_to/use_estimator.rst (convert to `.mdx`)
- [ ] https://github.com/Qiskit/qiskit/blob/main/docs/how_to/use_sampler.rst (convert to `.mdx`)`

### Files to migrate to docs/run
- [ ] https://github.com/Qiskit/qiskit-tutorials/blob/master/tutorials/circuits_advanced/08_gathering_system_information.ipynb

### Files to migrate to docs/other
- [ ] https://github.com/Qiskit/qiskit/blob/main/docs/faq.rst (convert to `.mdx`)

Note: the following pages should not be moved over:

• https://github.com/Qiskit/qiskit/blob/main/docs/qc_intro.rst
• https://github.com/Qiskit/qiskit/blob/main/docs/intro_tutorial1.rst

[Eric-Arellano]

All that's left are the migration guides, which are going to require some rewriting of content. Tracked by #213.