Decouple JS SDK from hardcoded Sirius Relayer constants

[EnchanterIO]

Due to shortage of time I hardcoded 2 hacks to OpenZeppelin node modules:

• const relay_lookup_limit_blocks = 1000;
• a RelayerURL "gsn.sirius.lightstreams.io" path in openzeppelin/gsn-provider node module dependency

File containing both hacks: node_modules/@openzeppelin/gsn-provider/src/tabookey-gasless/RelayClient.js

I added comments and will fix this in the incoming weeks but this will do for the moment.

These changes will be automatically applied by a post-install script using a patching strategy.