Usability: Improve Error in ErrorIfCoordinatorNotAddedAsWorkerNode

When coordinator is not added to the cluster as a worker when it should be, we give an error:

```psql
[local] talha@talha:9700-5789=# select create_citus_local_table('citus_local');
ERROR: could not find the coordinator node in metadata as it is not added as a worker
Time: 1.120 ms
```

Here it might not be clear for some users what to do.

I think it would be nice to give a hint to show what to run such as

```
To add the coordinator, run `SELECT 1 FROM master_add_node(, , groupid => 0);`
```
(We can dynamically find the ip and port and replace them in the command)

Maybe it is not desirable to add the coordinator, if so, we can also mention that in this hint/error.