Unable to retrieve Schema for Data connector, unsure what to do next

### Component

Impacts CLI/Connectors

### What is the current behaviour?

Added a data connector (postgres, called CRM, in a subgraph called MongoDB - don't ask) and when I attempt to update the connector link, it says it can't read the schema, I am unsure what to do next.

9:32AM ERR Unable to retrieve schema for DataConnectorLink "crm" in Subgraph config "/Users/jmartin/Development/Hasura/demos/mongo-atlas/ddn/mongodb/subgraph.yaml": Error fetching schema: Get "http://local.hasura.dev:8085/schema": dial tcp 127.0.0.1:8085: connect: connection refused

### What is the expected behaviour?
Provide a hint where to look. Is there an auth issue, is the server down, etc.

### How to reproduce the issue?

1. Run a local postgres instance and expose it on port something like 9999
2. Run the connector steps to add the postgres instance
3. Attempt to update

### Please provide any traces or logs that could help here.

From the monodb_crm connector container

```
error initializing connector state: unable to initialize connection pool: pool timed out while waiting for an open connection
{"timestamp":"2024-07-14T21:05:34.576327Z","level":"ERROR","fields":{"meta.signal_type":"log","event.domain":"ndc","event.name":"Initialization error","name":"Initialization error","body":"error initializing connector state: unable to initialize connection pool: pool timed out while waiting for an open connection","error":true},"target":"ndc_postgres::connector"}
{"timestamp":"2024-07-14T21:06:45.497730Z","level":"ERROR","fields":{"meta.signal_type":"log","event.domain":"ndc","event.name":"Initialization error","name":"Initialization error","body":"error initializing connector state: unable to initialize connection pool: pool timed out while waiting for an open connection","error":true},"target":"ndc_postgres::connector"}
error initializing connector state: unable to initialize connection pool: pool timed out while waiting for an open connection
```

### Any possible solutions/workarounds you're aware of?

Unknown

### Keywords

DX

Start by reproducing the CLI connector-link update with the local Postgres setup and inspect the subgraph config at demos/mongo-atlas/ddn/mongodb/subgraph.yaml. Compare the connection-refused error for 127.0.0.1:8085 with the connector container's connection-pool timeout. Done means the failure provides an actionable hint about the unavailable server, authentication, or connection configuration.

Written by the indexing model from the issue text.