[Feature Request] Allow a user to connect their Discord account to their Portal account

# Overview
Set up the groundwork for future discord integration features. This groundwork includes grabbing user metadata, such as snowflake, username, and discriminator, from discord,

A user must first connect a Discord account. On each sign-in afterward, we need to fetch the user's metadata from Discord including their snowflake. This is done by using the access token in the accounts collection to send an api call to Discord.
# Tasks
- [x] Add Discord Auth URL with identify, email, guilds scope to NextAuth Discord provider options
- [ ] Get user metadata from Discord, including snowflake, username, discriminator
- [ ] [Verify user is in acm server](https://github.com/acmutd/portal-backend/blob/b596d0f2caa2db947df7b78182296c8f0b246c9a/functions/src/admin/discord.ts#L25)
- [ ] [Add verified role](https://github.com/acmutd/portal-backend/blob/b596d0f2caa2db947df7b78182296c8f0b246c9a/functions/src/admin/discord.ts#L84)
- [ ] Document

# Supplemental Information
* [NextAuth Discord Provider Options Docs](https://next-auth.js.org/providers/discord)
* [portal v1 getting user metadata](https://github.com/acmutd/portal-backend/blob/b596d0f2caa2db947df7b78182296c8f0b246c9a/functions/src/admin/auth0.ts#L51)
* [portal v1 discord features](https://github.com/acmutd/portal-backend/blob/dev/functions/src/admin/discord.ts)

Review `functions/src/admin/discord.ts` and the linked `functions/src/admin/auth0.ts` first; they show existing metadata and role patterns. Then find the NextAuth Discord provider configuration in the auth flow and update scope options (identify, email, guilds), and trace where access tokens are stored so each sign-in can call Discord for `snowflake`, `username`, and `discriminator`. Run or replay the sign-in path through that auth entry point to validate token use end to end. Done when each login fetches metadata, checks ACM guild membership, applies the verified role via `discord.ts`, and updates docs.

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