[explorer] Show the miner name in the block page
Summary:
T3543
Parse coinbase string for miner. Display on block page.
Test Plan:
cd explorer-exe cargo run
check rendering for a few blocks
cd explorer-server cargo test
tests pass
Reviewers: #bitcoin_abc, tobias_ruck
Reviewed By: #bitcoin_abc, tobias_ruck
Subscribers: tobias_ruck, PiRK, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D16533