feat: allow configuring OIDC email claim and OIDC auth url parameters (#6867)

This commit:

- Allows configuring the OIDC claim Coder uses for email addresses (by default, this is still email)
- Allows customising the parameters sent to the upstream identity provider when requesting a token. This is still access_type=offline by default.
- Updates documentation related to the above.

docs/api/general.md

@@ -231,9 +231,11 @@ curl -X GET http://coder-server:8080/api/v2/deployment/config \
     },
     "oidc": {
       "allow_signups": true,
+      "auth_url_params": {},
       "client_id": "string",
       "client_secret": "string",
       "email_domain": ["string"],
+      "email_field": "string",
       "group_mapping": {},
       "groups_field": "string",
       "icon_url": {