website: upgrade mike to version 2.0

https://github.com/jimporter/mike

The main immediate advantage of this is that `mike` will stop pushing empty
commits.

Also, we can consider switching to using symlinks instead of redirects for
mapping the "latest" version to "v0.11.0". This would make
`https://martinvonz.github.io/jj/latest/` have the same content as
`https://martinvonz.github.io/jj/v0.11.0/` (until the next version is out), but
the user would see `latest` in the URL.

For now, I set an option to keep using redirects.

I did a bit of non-exhaustive testing; it seems to work.

.github/scripts/docs-build-deploy

@@ -12,4 +12,6 @@ export "SITE_URL_FOR_MKDOCS=$1"; shift
 # https://github.com/python-poetry/poetry/issues/1917
 export PYTHON_KEYRING_BACKEND=keyring.backends.fail.Keyring
 poetry install  # Only really needed once per environment unless there are updates
-poetry run -- mike deploy "$@"
+# TODO(ilyagr): The new default "alias-type" is symlink, we should consider
+# switching to it.
+poetry run -- mike deploy --alias-type redirect "$@"

pyproject.toml

@@ -20,7 +20,7 @@ mdx-breakless-lists = "^1.0.1"
 # Allows setting up redirects when renaming docs files
 mkdocs-redirects = "^1.2.1"
 # Versioning of documentation
-mike = "^1.1.2"
+mike = "^2.0.0"
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]