Fix/validate access token user not found (#8484)

# Description
Closes #7244 

See details about implementation:
#7244 (comment)
and
#7244 (comment)

# Changes
- return a `USER_NOT_FOUND` error instead of `INVALID_INPUT` error
- tweak unit tests to correctly test `AuthExceptionCode`, as it wasn't
properly tested; it was actually a _false positive_. This is because
[`toThrow`](https://jestjs.io/docs/expect#tothrowerror) from jest only
checks the `message`, and not any other method / attributes from the
`Error`. It's a know behaviour and not considered a bug, see
jestjs/jest#13232 (comment)

packages/twenty-server/src/engine/core-modules/auth/strategies/jwt.auth.strategy.spec.ts

@@ -151,8 +151,13 @@ describe('JwtAuthStrategy', () => {
     );
 
     await expect(strategy.validate(payload as JwtPayload)).rejects.toThrow(
-      new AuthException('User not found', AuthExceptionCode.INVALID_INPUT),
+      new AuthException('User not found', expect.any(String)),
     );
+    try {
+      await strategy.validate(payload as JwtPayload);
+    } catch (e) {
+      expect(e.code).toBe(AuthExceptionCode.USER_NOT_FOUND);
+    }
   });
 
   it('should be truthy if type is ACCESS, no jti, and user exist', async () => {

packages/twenty-server/src/engine/core-modules/auth/strategies/jwt.auth.strategy.ts

@@ -113,7 +113,7 @@ export class JwtAuthStrategy extends PassportStrategy(Strategy, 'jwt') {
     if (!user) {
       throw new AuthException(
         'User not found',
-        AuthExceptionCode.INVALID_INPUT,
+        AuthExceptionCode.USER_NOT_FOUND,
       );
     }