console: allow creating remote joins from and to the same remote schema

### Version Information

2.18.x
### Environment

All

### What is the current behaviour?

In the console when creating a remote relationship on a remote schema, the console UI filters out the source remote schema as an option for creating the relationship. The server allows this to happen (can be tested via the API or metadata).

### What is the expected behaviour?

The console should allow the source remote schema to also be a target in a remote relationship.

### How to reproduce the issue?

1. Add a remote schema to Hasura, preferably with two types that can be joined.
2. Try creating a remote relationship and check the dropdown of the target.
3.
### Screenshots or Screencast

Start by reproducing remote relationship creation in the console with a remote schema containing two joinable types, then inspect the target-schema dropdown behavior. Done means the source remote schema is available as a target and a relationship can be created through the console, matching the server's existing API and metadata behavior.

Written by the indexing model from the issue text.