Indexer crashing on multiple websocket endpoints

[bz888]

Prerequisites

• Are you running the latest version(s)?
• Have you searched the documentation for your issue?
• Did you search for an existing issue or pull request?

Description

When using multiple websocket endpoints, if one of the socket is closed or throws an error, the indexer would crash.

Details

To reproduce, use two endpoints, one does not connect and one that does. When running it, it should throw a connection error.

[UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "Connection attempt timed out after 10009 ms".] {
  code: 'ERR_UNHANDLED_REJECTION'
}

Steps to Reproduce

This can be replicated with any subquery project, just need to find a non-connecting endpoint and a connecting on (websocket)
Expected behavior: [What you expected to happen]
Indexer should not crash even if one of the endpoints is broken
Actual behavior: [What actually happened]
Indexer crashes if one of the endpoints is broken

Any other information

Is there any other information you would like to add?

[yoozo]

There are similar error messages, I think this is a configuration error.