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/routes/api/users.ts

@@ -5,6 +5,7 @@ import userInviter from "@server/commands/userInviter";
 import userSuspender from "@server/commands/userSuspender";
 import { sequelize } from "@server/database/sequelize";
 import InviteEmail from "@server/emails/templates/InviteEmail";
+import env from "@server/env";
 import { ValidationError } from "@server/errors";
 import logger from "@server/logging/logger";
 import auth from "@server/middlewares/authentication";
@@ -338,11 +339,11 @@ router.post("users.resendInvite", auth(), async (ctx) => {
     user.incrementFlag(UserFlag.InviteSent);
     await user.save({ transaction });
 
-    if (process.env.NODE_ENV === "development") {
+    if (env.ENVIRONMENT === "development") {
       logger.info(
         "email",
         `Sign in immediately: ${
-          process.env.URL
+          env.URL
         }/auth/email.callback?token=${user.getEmailSigninToken()}`
       );
     }