[intercom] Explicit setting of integrations prevents sending of `user_hash`.

Migrated from #10 by @more-ron

We a have a code that dynamically turns on or off Intercom integration depending on the user.

We hit a condition when it should send it to Intercom but it doesn't. It does try to send it but it's missing the user_hash.

        analytics.identify('id', { ... }, {
          Intercom: { user_hash: 'x' },
          integrations: {
            All: true,
            ...,
            Intercom: true
          }
        });

Removing the explicit setting fixed it.

        analytics.identify('id', { ... }, {
          Intercom: { user_hash: 'x' },
          integrations: {
            All: true,
            ...
          }
        });

However that just a work around and it makes the backend code a bit more complicated now that it has to decide to include the Intercom key rather than just setting the value to either true or false.

It's also setting a trap for developers expecting it to just work.

Start by tracing how identify options handle explicit integration settings, then follow the Intercom integration path using the two payload examples in this issue. Reproduce the case where Intercom is explicitly true and verify that the supplied user_hash is still sent; done means the explicit setting no longer drops it.