fix: use unique ID for linked accounts (#3441)

- move OAuth-related fields off of api_keys into a new user_links table
- restrict users to single form of login
- process updates to user email/usernames for OIDC
- added a login_type column to users

coderd/database/queries/user_links.sql

@@ -0,0 +1,46 @@
+-- name: GetUserLinkByLinkedID :one
+SELECT
+	*
+FROM
+	user_links
+WHERE
+	linked_id = $1;
+
+-- name: GetUserLinkByUserIDLoginType :one
+SELECT
+	*
+FROM
+	user_links
+WHERE
+	user_id = $1 AND login_type = $2;
+
+-- name: InsertUserLink :one
+INSERT INTO
+	user_links (
+		user_id,
+		login_type,
+		linked_id,
+		oauth_access_token,
+		oauth_refresh_token,
+		oauth_expiry
+	)
+VALUES
+	( $1, $2, $3, $4, $5, $6 ) RETURNING *;
+
+-- name: UpdateUserLinkedID :one
+UPDATE
+	user_links
+SET
+	linked_id = $1
+WHERE
+	user_id = $2 AND login_type = $3 RETURNING *;
+
+-- name: UpdateUserLink :one
+UPDATE
+	user_links
+SET
+	oauth_access_token = $1,
+	oauth_refresh_token = $2,
+	oauth_expiry = $3
+WHERE
+	user_id = $4 AND login_type = $5 RETURNING *;