py version support policy for RHEL: only track full support releases

Allow for any supported version of Python, not just the default Python version

This would mean that we can then drop Python 3.6 support

docs/pythonversions.rst

@@ -2,16 +2,16 @@
 Python version support policy
 =============================
 
-Cwltool will always support `stable Python 3 releases with active branches
-<https://devguide.python.org/#status-of-python-branches>`_.
+`cwltool` will always support `Python 3 versions that are officially supported by the Python Software Foundation
+<https://devguide.python.org/versions/#versions>`_.
 
-For versions that are no longer supported by Python upstream, cwltool
-support also extends to the default Python version included in the
+For versions that are no longer supported by the Python Software Foundation (or "upstream" for short), cwltool
+support also extends to the latest Python versions included in the
 following major Linux distributions:
 
-* Debian (`stable <https://wiki.debian.org/DebianStable>`_, `oldstable <https://wiki.debian.org/DebianOldStable>`_)
+* Debian (`stable <https://www.debian.org/releases/>`_)
 * Ubuntu (`LTS release standard support <https://wiki.ubuntu.com/Releases>`_)
-* Centos 7 (`while in maintenance <https://wiki.centos.org/About/Product>`_)
+* RHEL (or binary compatible) (`full support releases <https://access.redhat.com/support/policy/updates/errata>`_) using packages from the main repo, or other distributor supported modules streams.
 
 If there is a conflict between a third party package dependency which
 has dropped support for a Python version that cwltool should support
@@ -22,32 +22,34 @@ and downstream users before making the decision to drop support for a
 Python version before the date outlined in this policy.  The reasoning
 for dropping support for a Python version should be outlined here.
 
-As of 2023-07-03, here are approximate cwltool support periods for
-across Python versions:
+As of 2023-08-08, here are approximate cwltool support periods for Python versions (`EOL` == "End of Life", the end of the support period by that provider):
 
 ====== ======================
 Python cwltool end of support
 ====== ======================
-2.7    ended January 2020
-3.5    ended October 2020
-3.6    2024-06 (Centos 7 EOL)
-3.7    2023-06-27 (upstream EOL)
+2.7    ended 2020-01 (upstream EOL)
+3.5    ended 2020-10 (upstream EOL)
+3.6    ended 2023-08-31 (change in cwltool policy)
+3.7    ended 2023-07-27 (upstream EOL)
 3.8    2025-04-02 (Ubuntu 20.04 LTS EOL)
-3.9    2025-11-05 (upstream EOL)
-3.10   2027-04-01 (Ubuntu 22.04 LTS EOL))
-3.11   2027-11-24 (upstream EOL)
+3.9    2025-10-01 (upstream EOL)
+3.10   2027-04-01 (Ubuntu 22.04 LTS EOL)
+3.11   2027-10-01 (upstream EOL)
+3.12   2028-10-01 (planned upstream EOL)
+3.13   2029-10-01 (planned upstream EOL)
 ====== ======================
 
-Default Python version of supported Linux distributions, for reference
-(as of February 2022)
-
-====== =============================================
-Python Linux distros where it is the default version
-====== =============================================
-3.6    Ubuntu 18.04 LTS, Centos 7
-3.7    Debian 10
-3.8    Ubuntu 20.04 LTS
-3.9    Debian 11
-3.10   Ubuntu 22.04 LTS
-3.11   Debian 12
-====== =============================================
+Python version of supported Linux distributions, for reference
+(as of August 2023)
+
+============== =============================================
+Python Version Linux distros where it is a supported version
+============== =============================================
+3.6            RHEL 7, Ubuntu 18.04 LTS
+3.7            Debian 10
+3.8            RHEL 8, Ubuntu 20.04 LTS
+3.9            Debian 11, RHEL 8, Ubuntu 20.04 LTS
+3.10           Ubuntu 22.04 LTS
+3.11           Debian 12, RHEL 9
+3.12           Debian 13 (planned)
+============== =============================================