[identity] Bump NONCE_TTL_DURATION to 15min

Summary: This addresses [ENG=9483](https://linear.app/comm/issue/ENG-9483/increase-siwe-nonce-lifetime).

Test Plan: Unit tests and CI... I think it's safe, I'm just changing a constant

Reviewers: bartek, varun, will

Reviewed By: bartek

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13584

services/identity/src/constants.rs

@@ -177,7 +177,7 @@ pub const KEYSERVER_PUBLIC_KEY: &str = "KEYSERVER_PUBLIC_KEY";
 // Nonce
 
 pub const NONCE_LENGTH: usize = 17;
-pub const NONCE_TTL_DURATION: Duration = Duration::from_secs(120); // seconds
+pub const NONCE_TTL_DURATION: Duration = Duration::from_secs(900); // seconds
 
 // Device list