Automatically build doc notebooks (#14718)

* Test workflow

* Build doc

* Make a clean build

* Add doc config

* Restore other workflows

* Final job

* Print something in else statements

* Pull before making changes

docs/source/_config.py

@@ -0,0 +1,7 @@
+INSTALL_CONTENT = """
+# Transformers installation ! pip install transformers datasets # To install from source instead of the last release,
+comment the command above and uncomment the following one. # ! pip install
+git+https://github.com/huggingface/transformers.git
+"""
+
+notebook_first_cells = [{"type": "code", "content": INSTALL_CONTENT}]