add upgrade guide for 4.2.0

Author: dandelany

docs/upgrade-guides/4-1-1-to-4-2-0.md

@@ -2,3 +2,31 @@
 
 This document describes the upgrade instructions from `4.1.1` to `4.2.0`.
 
+## Repository Renames
+This is our first release since renaming our core code repositories to [`plandev`](https://github.com/NASA-AMMOS/plandev),
+[`plandev-ui`](https://github.com/NASA-AMMOS/plandev-ui), 
+[`plandev-gateway`](https://github.com/NASA-AMMOS/plandev-gateway) and 
+[`plandev-docs`](https://github.com/NASA-AMMOS/plandev-docs).
+
+This was communicated previously, and redirects from the old URLs are in place, so we do not expect any user impact from this change. 
+However, it's a good idea to update any old references in your code or documents to their new names.
+
+## DB Migrations
+Multiple DB migrations were added in this release. If you are upgrading from a past version and want to preserve your data, follow the instructions in the
+[Database Migrations Guide](../deployment/advanced-database-migrations.mdx) to apply migrations after upgrading. Make sure to either pass the `--all` flag, or apply **all** migrations interactively.
+
+## SeqDev Action Versioning
+SeqDev 4.2.0 includes a new UI for managing and running actions, and a new **versioned Actions** feature. Instead of uploading
+a new action every time you make a change, you can now add a new version of an existing Action in the UI by opening it in your Workspace
+and clicking "Upload New Version" in the top left. You can also deprecate old versions of actions by clicking "Archive Version" on the
+action's "Configure" page - this will preserve records of previous runs from this version, but prevent users from running it in future.
+
+## SeqDev Workspace File Metadata
+This SeqDev release adds support for saving additional metadata alongside your workspace files. SeqDev will automatically maintain some metadata,
+such as "created by" and "last edited by", while allowing users to store additional arbitrary JSON-shaped metadata in a `user` field, accessible
+via the UI or the [`aerie-actions` API v1.2.4](https://github.com/NASA-AMMOS/aerie-actions/releases). We also keep a "read-only" flag in metadata
+which, when set by the user, will prevent files from being accidentally overwritten or deleted.
+
+Note that this metadata is stored in our Docker file system volume as hidden `.meta.seqdev` files alongside the regular Workspace files. If you do any
+manual manipulation of these files in the filesystem (ie. not using the UI or API), make sure to maintain their associated `.meta.seqdev` files or the
+file metadata may be lost.