Add Blockstream Fee Analysis Script

[FrancisPouliot]

Like issue #75 we should add this when we get a response from a txid we're watching, or coins coming in or out.

The idea is to have the fee analysis included as a field in the "unconfirmed-tx" and "confirmed-tx" callback responses and also a standalone API endpoint

[FrancisPouliot]

The scripts can be found here https://github.com/Blockstream/esplora/blob/master/client/src/lib/fees.js

[Kexkey]

@mjmohammadi1 what do you think about this feature for you? It's pretty straightforward, just convert the algo from JS to shell script and add results to the POSTed content of the webhooks/callbacks on watched addresses. Let me know if you need assistance on that.

[mjmohammadi1]

@Kexkey I'm interested in it , I was always passionate about learning shell scripts.