citus_update_node wrong behaviour

Hello.
I want to be able to use the same nodename / nodeport combination for different node roles. It will allow me to build a robust fault-tolerant workers cluster (not only for the PRIMARY DB, but also for replicas with `noderole = 'secondary'`).

Existing `pg_dist_node`'s UNIQUE constraint is something like `(nodename, nodeport)`, but it should be `(nodename, nodeport) WHERE noderole = 'primary'`.

See more detailed explanation in [citus-users](https://groups.google.com/g/citus-users/c/jo-pAg4yeP8) group.

P.s.
```
Citus 11.2.0 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0, 64-bit
PostgreSQL 14.7 (Ubuntu 14.7-1.pgdg18.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0, 64-bit

```