docs(docker-compose): documentation to assist database upgrades of docker-compose (#1100)

Upgrading databases in postgres is not straightforward as the volume is often not compatible. It
requires creating a database backup, deleting the volume, deploying the upgraded version, and then
restoring from backup. This PR provides documentation and scripts to assist with this process.

Co-authored-by: Fabians <fabis94@live.com>

docs/migrations/README.md

@@ -0,0 +1,5 @@
+# Migrations
+
+These documents assist with migrating Speckle between clusters or between versions.
+
+- Postgres

docs/migrations/postgres/README.md

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+# Migrations - Postgres
+
+## docker-compose
+
+Backing up and restoring postgres data stored in our local development docker volumes when upgrading to new postgres versions.
+
+### Using pgadmin
+
+1. _If postgres is already running, you can skip this step._ To get it running, please first checkout this repository at the commit or tag used to previously deploy Speckle on docker-compose. For example, using `git` on the command line to checkout tag `2.8.0`:
+
+   ```shell
+   git fetch --all --tags
+   git checkout tags/2.8.0 -b main
+   ```
+
+1. _If postgres is already running, you can skip this step._ Start the dependencies, which include postgres and pgadmin:
+
+   ```shell
+   docker-compose --file ./docker-compose-deps.yml up --detach
+   ```
+
+1. Verify that they are running:
+
+   ```shell
+   docker ps
+   ```
+
+1. Open the [postgres admin (pgadmin) dashboard](http://127.0.0.1:16543/). If you have changed the configuration of pgadmin, you can find it by running `docker ps` and making a note of the address and port it is serving.
+1. The user name and password can be found in [`./docker-compose-deps.yml`](../../../docker-compose-deps.yml), next to `PGADMIN_DEFAULT_EMAIL` and `PGADMIN_DEFAULT_PASSWORD`.
+   - At the time of writing the email is `admin@localhost.com` and the password `admin`.
+1. Click `add new server`
+1. In the dialog box in the `General` tab, enter the name `docker-compose` (or any other value that you wish).
+1. In the dialog box in the `Connection` tab:
+   - for the `Host name/addresses` enter `postgres` (its the name of the postgres container in the docker-compose config)
+   - for `port`, use `5432` (you can check this is port number used for the `postgres` container in [`./docker-compose-deps.yml`](../../../docker-compose-deps.yml))
+   - for `database`, `username`, and `password` use the values in the file assigned to the respective `POSTGRES_DB`, `POSTGRES_USER`, and `POSTGRES_PASSWORD` keys. By default the value of these are all `speckle`.
+1. Click `save`
+1. You can now select the database from the browser window (typically found on the left hand side). Expand `docker-compose` and `databases`, the right-click on the database you wish to backup.
+1. Choose a filename and start the backup process.
+1. Once the backup is done, make sure you click on the "Click to open file location" button and download the backup to your host machine.
+1. We recommend testing the integrity of the backup at this time. One means of doing this is to install speckle-server on another machine (or modify the name and ports in the file and install a second locally), then upload the backup per the below instructions using pgadmin. Use pgadmin or Speckle to check that the information is present.
+1. Stop the docker-compose dependencies with:
+
+   ```shell
+   docker-compose -f ./docker-compose-deps.yml down
+   ```
+
+1. Find the name of the postgres database volume.
+
+   ```shell
+   docker volume ls
+   ```
+
+1. ⚠️ Delete the postgres database. This is destructive, please ensure that the backup is correct and saved securely before proceeding, see instructions above. ⚠️
+
+   ```shell
+   docker volume rm speckle-server_postgres-data
+   ```
+
+1. Check out the version of Speckle Server you wish to deploy. For example, using `git` on the command line to checkout the latest commit or a tagged version:
+
+   ```shell
+   git checkout main
+   ```
+
+   ```shell
+   git checkout tags/2.9.0 -b main
+   ```
+
+1. Deploy the docker-compose file with the updated postgres version:
+
+   ```shell
+   docker-compose -f ./docker-compose-deps.yml up --detach
+   ```
+
+1. Open pgadmin and connect to the server, using the instructions above.
+1. Right click `databases` from the browser window, and click `create`.
+1. Right click the created database and click `restore`, selecting your previously stored backup. You will need to upload the backup you previously downloaded back into pgadmin first.
+1. Deploy Speckle server, if necessary, and verify the data is correct.