core, miner: add debug logs to track chain insertion

[manav2401]

This PR adds debug logs for the ongoing sync issues

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 55.98%. Comparing base (2dd9973) to head (e413a50).
Report is 1 commits behind head on v1.2.7-beta-candidate.

Files	Patch %	Lines
core/blockchain.go	80.00%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           v1.2.7-beta-candidate    #1166      +/-   ##
=========================================================
+ Coverage                  55.90%   55.98%   +0.08%     
=========================================================
  Files                        658      658              
  Lines                     114435   114488      +53     
=========================================================
+ Hits                       63974    64097     +123     
+ Misses                     46600    46542      -58     
+ Partials                    3861     3849      -12     

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