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.

coderd/coderdtest/coderdtest.go

@@ -967,6 +967,8 @@ func (o *OIDCConfig) OIDCConfig(t *testing.T, userInfoClaims jwt.MapClaims, opts
 		}),
 		Provider:      provider,
 		UsernameField: "preferred_username",
+		EmailField:    "email",
+		AuthURLParams: map[string]string{"access_type": "offline"},
 		GroupField:    "groups",
 	}
 	for _, opt := range opts {