Make sure node id is constant for sync node. Add common_bls_key to the schain config

[badrogger]

Changes:

1. Do not change node id after rotation.
2. Add common_bls_key to the schain config.

Tests:

1. Fixed corresponding unit tests.
2. Tested on local network.

Performance:

1. No performance related changes were introduced.

[codecov]

Codecov Report

Attention: Patch coverage is 78.72340% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 81.59%. Comparing base (0ed6b90) to head (b9157e9).

Files	Patch %	Lines
sync_node.py	0.00%	8 Missing ⚠️
core/node_config.py	83.33%	1 Missing ⚠️
core/schains/config/generator.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           v2.7.x    #1066      +/-   ##
==========================================
- Coverage   81.65%   81.59%   -0.06%     
==========================================
  Files         103      103              
  Lines        5946     5971      +25     
==========================================
+ Hits         4855     4872      +17     
- Misses       1091     1099       +8     

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