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/logging/sentry.ts

@@ -27,7 +27,7 @@ export function requestErrorHandler(error: any, ctx: ContextWithState) {
     return;
   }
 
-  if (process.env.SENTRY_DSN) {
+  if (env.SENTRY_DSN) {
     Sentry.withScope(function (scope) {
       const requestId = ctx.headers["x-request-id"];