[Chronik] Add failover.ts integration test to chronik-client

Summary:
We spin up 3 nodes using Python, and then stop them 1 by 1 to test the failover works.

We check to make sure the failover is working by:

Connect to a new node after we force current node to stop.

Assert that the node is indeed stopped.

Mine a block on new node, ensure we still receive subscription updates.

Call blockchain.info() on the node.

Test Plan:
cd modules/chronik-client/test
npx mocha -j1 -r ts-node/register test/integration/failover.ts

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18264