Add release notes for 4.2.2

docs/releases/4.2.2.rst

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+============================
+Release notes for IRRd 4.2.2
+============================
+
+IRRd 4.2.2 was released on December 2nd, 2021, and fixes two issues that
+occurred in 4.2.1:
+
+* If users created multiple objects with the same RPSL primary key, in the
+  same source, with different object classes, IRRD would only
+  `import one of them and discarded the other`_. This could occur, for example,
+  when a `mntner` and `as-set` had the same name. This issue was quite rare.
+* When running on PyPy, IRRD had
+  `infinite file descriptor growth`_ when using PyPy, causing it to run out
+  of file descriptors eventually regardless of configured limits.
+* IRRD `was unable to run in the foreground with stdout logging`_.
+* IRRD would `reject the autogenerated last-modified attribute`_ in submitted 
+  objects, which was confusing to users.
+
+.. _import one of them and discarded the other: https://github.com/irrdnet/irrd/issues/450
+.. _infinite file descriptor growth: https://github.com/irrdnet/irrd/issues/578
+.. _was unable to run in the foreground with stdout logging: https://github.com/irrdnet/irrd/issues/557
+.. _reject the autogenerated last-modified attribute: https://github.com/irrdnet/irrd/issues/587
+
+Steps required to upgrade
+-------------------------
+You must run the :ref:`irrd_database_upgrade <deployment-database-upgrade>`
+command after updating your installed version of IRRD.
+
+Follow these steps to upgrade:
+
+* Disable all cron and e-mail triggered tasks. There should be no calls
+  to any IRRd scripts during the upgrade process.
+* Upgrade your installed version of IRRD to 4.2.2.
+* Run :ref:`irrd_database_upgrade <deployment-database-upgrade>`. This may take
+  several minutes.
+* Start IRRd and re-enable the cron / e-mail triggered tasks.
+
+Between the time that the upgrade finishes and IRRD is restarted, mirroring
+processes may fail. This will automatically recover after the restart.
+
+The underlying reason is that if your database version is inconsistent with the
+version of running IRRD code, inserting or updating RPSL objects will fail.
+Therefore, user updates received over e-mail should be paused during the time
+these may be inconsistent
+
+As with all other database upgrades, you can also choose to shut down IRRD
+entirely during the database upgrade.
+
+Downgrading from 4.2.2 to 4.2.1
+-------------------------------
+If you are running IRRd 4.2.2, and would like to downgrade back to 4.2.1,
+the database schema needs to be modified. You can either restore an older
+copy of your database, start with a fresh database, or use the database
+migrations.
+
+If you want to use the database migrations, run this command **before**
+downgrading your local package installation to 4.2.1::
+
+    irrd_database_downgrade --version 893d0d5363b3
+
+If you would like to re-upgrade to 4.2.2 later on, you will need to run
+the database migrations again, as listed in the upgrade steps.