Set up docs redirects

Create a redirects file and set up automation to apply it to the RTD
project.

The file is initialized with existing redirects, fetched with:

    rtd --json projects nextstrain-augur redirects \
      | yq '.[] | [{"type": "page", "from_url": .from_url, "to_url": .to_url}]' \
      | sed 's/"//g'

.github/workflows/sync-redirects.yaml

@@ -0,0 +1,30 @@
+name: Sync RTD redirects
+
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - docs/redirects.yaml
+      - .github/workflows/sync-redirects.yaml
+
+  # Manually triggered using GitHub's UI
+  workflow_dispatch:
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+
+      - name: Upgrade Python toolchain
+        run: python3 -m pip install --upgrade pip setuptools wheel
+
+      - name: Install readthedocs-cli
+        run: python3 -m pip install readthedocs-cli
+
+      - name: Sync redirects
+        run: rtd projects nextstrain-augur redirects sync -f docs/redirects.yaml --wet-run
+        env:
+          RTD_TOKEN: ${{ secrets.RTD_TOKEN }}

docs/redirects.yaml

@@ -0,0 +1,57 @@
+# Authoritative list of redirects we have configured in RTD.  See the
+# docs.nextstrain.org repo's README.md¹ for more information on maintaining
+# redirects.
+#
+# ¹ https://github.com/nextstrain/docs.nextstrain.org#configuring-redirects
+---
+- type: page
+  from_url: /faq/augur_snakemake.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/augur_snakemake.html
+
+- type: page
+  from_url: /faq/colors.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/colors.html
+
+- type: page
+  from_url: /faq/community_hosting.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/share/community-builds.html
+
+- type: page
+  from_url: /faq/fasta_input.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/fasta_input.html
+
+- type: page
+  from_url: /faq/import-beast.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/import-beast.html
+
+- type: page
+  from_url: /faq/lat_longs.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/lat_longs.html
+
+- type: page
+  from_url: /faq/seq_traits.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/seq_traits.html
+
+- type: page
+  from_url: /faq/translate_ref.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/translate_ref.html
+
+- type: page
+  from_url: /faq/vcf_input.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/vcf_input.html
+
+- type: page
+  from_url: /tutorials/tb_tutorial.html
+  to_url: https://docs.nextstrain.org/en/latest/tutorials/tb_tutorial.html
+
+- type: page
+  from_url: /tutorials/tutorials.html
+  to_url: https://docs.nextstrain.org/en/latest/tutorials/index.html
+
+- type: page
+  from_url: /tutorials/zika_tutorial.html
+  to_url: https://docs.nextstrain.org/en/latest/tutorials/zika_tutorial.html
+
+- type: page
+  from_url: /usage/augur_snakemake.html
+  to_url: https://docs.nextstrain.org/en/latest/guides/bioinformatics/augur_snakemake.html