ADR 29: Standardize database connections

[razvan]

Triggered by stackabletech/hive-operator#148

Fixes stackabletech/issues#238

[sbernauer]

Quick pass, just doing minor writing stuff.
Some questions, just writing them down, would suggest to have a call about them:

1. Is DatabaseConnection namespaced? Would be fine for me. If not we would have to use a SecretClass as Secrets are namespaced
2. What do you think of a complex enum within DatabaseConnection?
3. I personally don't like putting something like driver pr protocol into the global CRD. That seems like a implementation detail of the individual product to me

Just throwing in an idea that should address the above points

apiVersion: databaseconnection.stackable.tech/v1alpha1
kind: DatabaseConnection
metadata:
    name: druid-metadata-connection
    namespace: default
spec:
  database:
    postgresql:
      host: druid-postgresql # mandatory
      port: 5432 # defaults to some port number - depending on wether tls is enabled
      schema: druid # defaults to druid
      credentials: druid-postgresql-credentials # mandatory. key username and password
      parameters: "" # optional
    redis:
      host: airflow-redis-master # mandatory
      port: 6379 # defaults to some port number - depending on wether tls is enabled
      schema: druid # defaults to druid
      credentials: airflow-redis-credentials # optional. key password. In case redis also supports usernames key username and password
      parameters: "" # optional
    derby:
      location: /tmp/derby/ # optional, defaults to /tmp/derby-{metadata.name}/derby.db
      parameters: "create=true" # optional

When we add tls support, things get more tricky

[netlify]

✅ Deploy Preview for stackable-docs ready!

Name	Link
🔨 Latest commit	fd414be
🔍 Latest deploy log	https://app.netlify.com/sites/stackable-docs/deploys/64e4bfcb238a3a000798b574
😎 Deploy Preview	https://deploy-preview-321--stackable-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[maltesander]

LGTM!