add double signed blocks metric

[YeahNotSewerSide]

Description

Add metric for a double signed blocks

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• New and existing E2E tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have not added any vulnerable dependencies to my code

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 59.72%. Comparing base (f8678d7) to head (7ea51e0).

Files with missing lines	Patch %	Lines
cmd/thor/node/node.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##           release/hayabusa    #1180   +/-   ##
=================================================
  Coverage             59.72%   59.72%           
=================================================
  Files                   266      266           
  Lines                 28136    28137    +1     
=================================================
+ Hits                  16803    16806    +3     
+ Misses                 9825     9824    -1     
+ Partials               1508     1507    -1     

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