feat(state-sync): drop old state parts at the end of epoch

[VanBarbascu]

The current gc logic cleans state part column along with the blocks. By default 5 epochs. State parts older than an epoch are not needed. This introduces a change to drop the state sync files at the end of the epoch.

[codecov]

Codecov Report

Attention: Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.75%. Comparing base (778b173) to head (63ef382).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
chain/chain/src/chain.rs	63.63%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12200      +/-   ##
==========================================
+ Coverage   71.72%   71.75%   +0.02%     
==========================================
  Files         834      833       -1     
  Lines      166616   166547      -69     
  Branches   166616   166547      -69     
==========================================
- Hits       119512   119501      -11     
+ Misses      41886    41825      -61     
- Partials     5218     5221       +3     

Flag	Coverage Δ
backward-compatibility	0.17% <0.00%> (+<0.01%)	⬆️
db-migration	0.17% <0.00%> (+<0.01%)	⬆️
genesis-check	1.25% <0.00%> (+<0.01%)	⬆️
integration-tests	38.74% <63.63%> (+0.01%)	⬆️
linux	71.41% <63.63%> (+0.02%)	⬆️
linux-nightly	71.32% <63.63%> (+0.02%)	⬆️
macos	54.43% <63.63%> (+0.02%)	⬆️
pytests	1.57% <0.00%> (+<0.01%)	⬆️
sanity-checks	1.37% <0.00%> (+<0.01%)	⬆️
unittests	65.57% <63.63%> (+0.02%)	⬆️
upgradability	0.21% <0.00%> (+<0.01%)	⬆️

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[saketh-are]

@VanBarbascu