Add Migration Guide for QuantumInstance (Qiskit#9554)

* Add draft

* Remove qiskit

* Add qi migration file

* Add content

* Finish content

* Update provider syntax

* Finish content

* Apply auto-suggestions

* Add doctests

* Change to dropdowns

* Add EM results

* Apply suggestions from code review

Co-authored-by: Steve Wood <40241007+woodsp-ibm@users.noreply.github.com>

* Apply review comments

* Apply suggestions from Declan's code review

Co-authored-by: Declan Millar <declan.millar@ibm.com>

* Apply suggestions from Guillermo's code review

Co-authored-by: Guillermo-Mijares-Vilarino <106545082+Guillermo-Mijares-Vilarino@users.noreply.github.com>

* Change from doctest to codeblocks

* Review follow-up edits

* Replace statevector with quantum info

* Reorder index

* Add assemble alternative

* Apply suggestions from Julien's code review

Co-authored-by: Julien Gacon <gaconju@gmail.com>

* Change transpilation example

* Apply suggestions from Juliencode review

Co-authored-by: Julien Gacon <gaconju@gmail.com>

---------

Co-authored-by: Steve Wood <40241007+woodsp-ibm@users.noreply.github.com>
Co-authored-by: Declan Millar <declan.millar@ibm.com>
Co-authored-by: Guillermo-Mijares-Vilarino <106545082+Guillermo-Mijares-Vilarino@users.noreply.github.com>
Co-authored-by: Julien Gacon <gaconju@gmail.com>

docs/migration_guides/index.rst

@@ -5,5 +5,6 @@ Qiskit Migration Guides
 .. toctree::
    :maxdepth: 1
 
-   opflow_migration
    algorithms_migration
+   opflow_migration
+   qi_migration