Fix/terminate node gracefully

[pavitthrap]

Description

Now, a copy of the bool should_keep_running, which manages system-wide shutdown, is owned by the BitcoinIndexer object.

In the function connect_handshake_backoff, this bool is now checked in every loop. The loop terminates if should_keep_running is false.

Applicable issues

• fixes stacks-node never terminates on Ctrl-C if bitcoind is unavailable #3734

Additional info (benefits, drawbacks, caveats)

Checklist

• Test coverage for new or modified code paths
• Changelog is updated

[codecov]

Codecov Report

Merging #3751 (a60d6fc) into develop (7a0e572) will decrease coverage by 0.91%.
The diff coverage is 90.54%.

@@             Coverage Diff             @@
##           develop    #3751      +/-   ##
===========================================
- Coverage    85.79%   84.88%   -0.91%     
===========================================
  Files          302      302              
  Lines       286529   286534       +5     
===========================================
- Hits        245830   243238    -2592     
- Misses       40699    43296    +2597     

Impacted Files	Coverage Δ
src/chainstate/coordinator/mod.rs	87.00% <50.00%> (+1.63%)	⬆️
src/burnchains/bitcoin/network.rs	81.44% <80.00%> (-0.04%)	⬇️
testnet/stacks-node/src/tests/neon_integrations.rs	59.39% <83.33%> (-23.99%)	⬇️
src/burnchains/bitcoin/indexer.rs	36.31% <88.57%> (+0.41%)	⬆️
...-node/src/burnchains/bitcoin_regtest_controller.rs	86.85% <100.00%> (+0.04%)	⬆️
testnet/stacks-node/src/neon_node.rs	82.21% <100.00%> (-1.66%)	⬇️
testnet/stacks-node/src/node.rs	89.61% <100.00%> (+5.18%)	⬆️
testnet/stacks-node/src/run_loop/neon.rs	83.15% <100.00%> (-0.32%)	⬇️
testnet/stacks-node/src/tests/epoch_22.rs	71.97% <100.00%> (-24.20%)	⬇️
testnet/stacks-node/src/tests/epoch_23.rs	99.63% <100.00%> (+<0.01%)	⬆️
... and 1 more

... and 42 files with indirect coverage changes

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[kantai]

LGTM!

[obycode]

LGTM!