feat: make default credentials for auth customizable

The current implementation defaults to username: `admin` and password: `zwave` when enabling auth. However, it can also be beneficial to make this customizable so that it can avoid some additional steps in updating these values.This is completely backwards compatible as well.

api/config/app.ts

@@ -16,8 +16,8 @@ export const backupsDir: string =
 export const nvmBackupsDir: string = joinPath(backupsDir, 'nvm')
 export const storeBackupsDir: string = joinPath(backupsDir, 'store')
 
-export const defaultUser: string = 'admin'
-export const defaultPsw: string = 'zwave'
+export const defaultUser: string = process.env.DEFAULT_USER || 'admin'
+export const defaultPsw: string = process.env.DEFAULT_PASSWORD || 'zwave'
 // lgtm [js/hardcoded-credentials]
 export const sessionSecret: string =
  process.env.SESSION_SECRET || 'DEFAULT_SESSION_SECRET_CHANGE_ME'