Migrate documentation and benchmarks from metapackage (Qiskit#10611)

### Summary

This cross-repository merge unifies the documentation, benchmarks and
code of conduct from the metapackage into Qiskit/Terra's build.

There are very non-trivial merge conflicts that have been resolved by
this commit. The summary is:

- `CODE_OF_CONDUCT.md`: taken directly from the metapackage's version.
- `docs/conf.py`: strongly unified, albeit without the translations
components that are added in a separate commit.
- `docs/index.rst`: taken almost verbatim from the metapackage. All the
API documentation RST files on Terra are moved to `docs/apidoc` (without
the trailing 's') to match the metapackage expectation, so the URLs of
built documentation will not change.
- `docs/release_notes.rst`: The metapackage's version is renamed to
`docs/legacy_release_notes.rst`, given a small introductory header, and
made an orphan linked only from a _new_ `docs/release_notes.rst` that
uses `reno`.
- `docs/tutorials.rst`: Mostly these were the same already. Updated to
include Qiskit/Terra's correction that it's not an orphan, and contain
the metapackage's extra intro tutorial.
- `docs/apidoc/terra.rst`: renamed to `docs/apidoc/index.rst` and
retitled to be correctly just "API Documentation".
- `requirements-dev.txt`: the version of the Sphinx theme is bumped to
1.14 to match the metapackage expectation.

Following merge commit ec5c9ca, there is a commit 66a5d9f that fixes
the ASV build for use in Terra, which is the rollup of the post-merge
commits of Qiskit#10546, which this PR supersedes.


### Details and comments

This should probably be merged ASAP before `main` moves on.

Resolutions on the metapackage:
- Fix Qiskit/qiskit-metapackage#1723
- Fix Qiskit/qiskit-metapackage#1722
- Fix Qiskit/qiskit-metapackage#1746

After this has merged, Qiskit#10610 should merge which will close the
remaining migration-related issues from the metapackage.

The metapackage was prepared for the migration using
[`git-filter-repo`](https://github.com/newren/git-filter-repo), with the
scripts and configuration files contained within
[metapackage_migration.zip](https://github.com/Qiskit/qiskit-terra/files/12324298/metapackage_migration.zip).
If you extract that zip, you need to activate a Python 3.11 `venv` then
run `metapackage_rewrite.bash` which will prepare the repo in the exact
state I merged to create this PR.

*edit*: In retrospect writing this, you might need to modify my script
so that it pulls only starting from commit
Qiskit/qiskit-metapackage@f131daf, which was the tip of `master` at the
time I ran this.

I tested the docs build locally and it looks as correct as I can tell.
There's still big cards pointing to experiments, dynamics etc on the
landing page, but I figured that enough's enough, and we can just fix
those last two things in Terra. This PR does not include
Qiskit/qiskit-metapackage#1791, which should be now cherry-picked onto
Terra.

Author: mtreinish

.gitignore

@@ -98,6 +98,7 @@ celerybeat-schedule
 .env
 
 # virtualenv
+.asv/
 .venv
 venv/
 ENV/

CODE_OF_CONDUCT.md

@@ -0,0 +1,25 @@
+{
+    "version": 1,
+    "project": "qiskit",
+    "project_url": "https://qiskit.org",
+    "repo": ".",
+    "install_command": [
+        "in-dir={env_dir} python -mpip install {wheel_file}[all] python-constraint qiskit-experiments==0.3.0"
+      ],
+    "uninstall_command": [
+        "return-code=any python -mpip uninstall -y {project}"
+    ],
+    "build_command": [
+        "pip install -U setuptools-rust",
+        "python setup.py build_rust --release",
+        "PIP_NO_BUILD_ISOLATION=false python -mpip wheel --no-deps --no-index -w {build_cache_dir} {build_dir}"
+    ],
+    "branches": ["main"],
+    "dvcs": "git",
+    "environment_type": "virtualenv",
+    "show_commit_url": "http://github.com/Qiskit/qiskit-terra/commit/",
+    "pythons": ["3.8", "3.9", "3.10", "3.11"],
+    "benchmark_dir": "test/benchmarks",
+    "env_dir": ".asv/env",
+    "results_dir": ".asv/results"
+}