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/utils/queue.ts

@@ -1,5 +1,6 @@
 import Queue from "bull";
 import { snakeCase } from "lodash";
+import env from "@server/env";
 import Metrics from "@server/logging/metrics";
 import Redis from "../redis";
 
@@ -18,7 +19,7 @@ export function createQueue(
           return Redis.defaultSubscriber;
 
         default:
-          return new Redis(process.env.REDIS_URL);
+          return new Redis(env.REDIS_URL);
       }
     },