Handle no-websocket error gracefully

[jrfrantz]

The light node says it supports polygon but crashes when you try to do it.
Cause is that there is no reservoir websocket URL for polygon (ie see src/types/index.ts:33 which only has goerli and mainnet).

This PR unbreaks polygon by not attempting to connect the websocket if an unsupported chain is used.

[r3lays]

Hey @jrfrantz! So the SyncNode did originally support Polygon. However we disabled it due to the fact that the WebSocket support for Polygon isn't out yet. As "asks" uses the WebSocket to handle the upkeeping.

The issue with running the SyncNode and not using the WebSocket is that it takes longer to get live/present "asks" to go into your database. This is due to the delay we have set of 1 minute (which is adjustable) to avoid hammering the API. We rely on the WebSocket to feed us realtime data, and we use the requests as a backup.

Good news is that Polygon support should be coming sometime this week. In any case, we can merge this since the SyncNode "asks" functionality will still work fine even without the WebSocket support.