Return more error details on http's read_response

[valentinewallace]

Otherwise helpful error information gets swallowed.

Closes #877

[codecov]

Codecov Report

Merging #919 (4f880c6) into main (fcc0723) will decrease coverage by 0.02%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##             main     #919      +/-   ##
==========================================
- Coverage   90.50%   90.48%   -0.03%     
==========================================
  Files          59       59              
  Lines       29769    29788      +19     
==========================================
+ Hits        26942    26953      +11     
- Misses       2827     2835       +8     

Impacted Files	Coverage Δ
lightning-block-sync/src/http.rs	95.11% <92.85%> (-0.27%)	⬇️
lightning-block-sync/src/rest.rs	67.24% <100.00%> (ø)
lightning-block-sync/src/rpc.rs	79.48% <100.00%> (ø)
lightning/src/ln/functional_tests.rs	96.89% <0.00%> (-0.11%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fcc0723...4f880c6. Read the comment docs.