✨ docs: Add guide on upgrading Python (#3624)

* ✨ guide

* 💄 put it first?

docs/guides/upgrade-python-version.md

@@ -0,0 +1,16 @@
+---
+status: new
+---
+
+To upgrade the version of Python used in the ETL pipeline, follow these steps on the ETL terminal:
+
+1. Remove the current environment configuration:
+   ```
+   rm -rf .venv
+   ```
+2. Rebuild the environment with the new Python version (replace xx.x with the desired version):
+   ```
+   PYTHON_VERSION=3.xx.x make .venv
+   ```
+
+The ETL currently supports versions 3.9 to 3.12.

mkdocs.yml

@@ -224,6 +224,7 @@ nav:
           - Regular updates: "guides/auto-regular-updates.md"
           - Pull requests: "guides/pull-requests.md"
       - Servers & settings:
+          - Upgrade Python version: "guides/upgrade-python-version.md"
           - Environments: "guides/environment.md"
           - Staging servers: "guides/staging-servers.md"
           - Public servers: "guides/sharing-external.md"