chore: Centralize env parsing, validation, defaults, and deprecation notices (#3487)

* chore: Centralize env parsing, defaults, deprecation

* wip

* test

* test

* tsc

* docs, more validation

* fix: Allow empty REDIS_URL (defaults to localhost)

* test

* fix: SLACK_MESSAGE_ACTIONS not bool

* fix: Add SMTP port validation

server/database/vaults.ts

@@ -1,9 +1,10 @@
 import SequelizeEncrypted from "sequelize-encrypted";
 import { Sequelize } from "sequelize-typescript";
+import env from "@server/env";
 
 /**
  * Encrypted field storage, use via the Encrypted decorator, not directly.
  */
 export default function vaults() {
-  return SequelizeEncrypted(Sequelize, process.env.SECRET_KEY);
+  return SequelizeEncrypted(Sequelize, env.SECRET_KEY);
 }