Clarify support lifecycle after JupyterLab 3 end of maintenance (#508)

* add JL3 EOL message to README.md

* add JL3 EOL message to the Users section of the readthedocs

* Fix links and messaging

* enable colon fence sphinx extension

* Update JupyterLab version requirements in README to >= 4.0 from >= 3.0

* Clarify requirements, add JL3

Author: andrii-i

README.md

@@ -14,7 +14,11 @@ details.
 
 ## Requirements
 
-- JupyterLab >= 3.0
+- JupyterLab 4.x (for newer Jupyter Scheduler versions)
+- JupyterLab 3.x (for Jupyter Scheduler 1.x)
+
+> [!IMPORTANT]
+> JupyterLab 3 will reach its end of maintenance date on May 15, 2024, anywhere on Earth. As a result, we will not backport new features to the v1 branch supporting JupyterLab 3 after this date. Fixes for critical issues will still be backported until December 31, 2024. If you are still using JupyterLab 3, we strongly encourage you to **upgrade to JupyterLab 4 as soon as possible**. For more information, see [JupyterLab 3 end of maintenance](https://blog.jupyter.org/jupyterlab-3-end-of-maintenance-879778927db2) on the Jupyter Blog.
 
 ## Install
 

docs/conf.py

@@ -14,6 +14,7 @@
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
 
 extensions = ["myst_parser"]
+myst_enable_extensions = ["colon_fence"]
 
 templates_path = ["_templates"]
 exclude_patterns = ["_build", "Thumbs.db", ".DS_Store"]

docs/users/index.md

@@ -26,6 +26,11 @@ jupyter labextension list
 and checking that both the `jupyter_scheduler` server extension and the
 `@jupyterlab/scheduler` prebuilt lab extension are enabled.
 
+:::{attention}
+:name: jupyter-lab-3-end-of-maintenance
+JupyterLab 3 will reach its end of maintenance date on May 15, 2024, anywhere on Earth. As a result, we will not backport new features to the v1 branch supporting JupyterLab 3 after this date. Fixes for critical issues will still be backported until December 31, 2024. If you are still using JupyterLab 3, we strongly encourage you to **upgrade to JupyterLab 4 as soon as possible**. For more information, see [JupyterLab 3 end of maintenance](https://blog.jupyter.org/jupyterlab-3-end-of-maintenance-879778927db2) on the Jupyter Blog.
+:::
+
 ## Use
 
 Jupyter Scheduler runs Jupyter notebooks in the background, either once or on a schedule. You can create _jobs_ (single run of an individual notebook) and _job definitions_ (scheduled recurring notebook jobs). When the scheduler runs your notebook, it makes a copy of the input file. The scheduler uses unique names for the input and output files so that rerunning the same notebook produces new files every time.