Un-cached account address data fetches might lead to rate limiting

[dboreham]

At present we're fetching validator handle data, and similar info from a github repo, like here:
https://github.com/0LNetworkCommunity/explorer/blob/main/api/src/ol/validators/validators.service.ts#L453
So the handle mapping file will be fetched from GitHub on every validator page load.

Problem with this, apart from performance, which at present probably isn't a big concern, is that GH might rate limit the traffic.