Handle Stale RPCs error for chains that have no RPCs

[sentry-io]

Sentry Issue: TALISMAN-EXTENSION-TWP

We know that GM has no RPCs, so we either shouldn't attempt to subscribe to it, or at least this error shouldn't end up in Sentry as unhandled

I think the reason why it's unhandled is because it's thrown inside Promise.race:

talisman/packages/chain-connector/src/ChainConnector.ts

Line 308 in 6e29f20

await Promise.race([

This is a similar situation to the one faced here, although in this case it is an Error being thrown, which suggests that the method used in that commit will not work to fix that problem. We should make a minimal reproduction case of errors thrown inside advanced Promise methods to understand how these should be handled.

Error: No healthy RPCs available for chain gm
  at chainConnector.connectChainSocket (../../packages/chain-connector/dist/talismn-chain-connector.esm.js:899:13)
  at chainConnector.subscribe (../../packages/chain-connector/dist/talismn-chain-connector.esm.js:747:26)

Error: RPCs are stale/unavailable for chain gm
  at Error: RPCs are stale (/unavailable for chain gm)

This error is occurring in the Portal as well as the extension.