Add initial Kubernetes config files

This includes all the resources currently running on https://gitea.kosmos.org

It sets up a persistent data volume for the MySQL database, one for the
Gitea data, that Gitea calls the custom folder (config, attachment,
avatars, logs, etc). We mount that persistent data volume as
/data/gitea. It also creates a Let's Encrypt certificate for
gitea.kosmos.org, also saved to the custom folder.

This also includes two scripts:

* `./script/get_secrets` downloads the secrets to the local filesystem so
they can be edited
* `./script/replace_secrets` deletes the remote secrets and creates them
again from the local ones in kubernetes/config/*

Closes #6

README.md

@@ -7,3 +7,34 @@ Feel free to [open issues] for questions, suggestions, bugs, to-do items, and
 whatever else you want to discuss or resolve.
 
 [open issues]: https://gitea.kosmos.org/kosmos/gitea.kosmos.org/issues
+
+## Kubernetes
+
+### Apply changes to resources
+
+```
+kubectl apply -f gitea-db.yaml
+kubectl apply -f gitea-server.yaml
+```
+
+### Write the secrets to the local filesystem
+
+```
+./script/get_secrets
+```
+
+It writes the secrets (currently the app.ini file, as well as auto-generated
+TLS certificates that are only used when no Let's Encrypt cert is available)
+to the `kubernetes/config/` folder. These files are not in Git because they
+contain credentials.
+
+Once you have edited them locally, you need to delete the secrets stored on
+Kubernetes before uploading them again. This is done by this script:
+
+```
+./script/replace_secrets
+```
+
+### Reuse a released persistent volume:
+
+https://github.com/kubernetes/kubernetes/issues/48609#issuecomment-314066616