Updates resyncIfBehind() functionality

[farazdagi]

What type of PR is this?

Other/Extension (due to amended assumptions)

What does this PR do? Why is it needed?

• Currently, resync only happens if node falls behind majority of finalized peers. In situations of long periods of non-finality, no peers will be far away, consequently resync never happens (so the 2nd stage of init-sync never re-triggered). This PR fixes that.

Which issues(s) does this PR fix?

Fixes #

Other notes for review

• We check peers to see if majority have some head slot towards which node can work. And when such peers are found -- resync is triggered.

[codecov]

Codecov Report

Merging #7039 into master will not change coverage.
The diff coverage is n/a.

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##           master    #7039   +/-   ##
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  Coverage   62.58%   62.58%           
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  Files         401      401           
  Lines       31722    31722           
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  Hits        19854    19854           
  Misses       9089     9089           
  Partials     2779     2779