catchup: increase HTTPFetcher fetcherMaxBlockBytes for larger block size

[cce]

Summary

When we grew the block size we did not adjust fetcherMaxBlockBytes to match, and it looks like we are running into this given errors like: response too large: 5265295 > 5242880.

Test Plan

Existing tests should pass.

[codecov]

Codecov Report

Merging #4569 (2b03964) into master (175d5aa) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4569      +/-   ##
==========================================
- Coverage   54.15%   54.15%   -0.01%     
==========================================
  Files         401      401              
  Lines       51628    51628              
==========================================
- Hits        27960    27959       -1     
- Misses      21319    21320       +1     
  Partials     2349     2349              

Impacted Files	Coverage Δ
catchup/universalFetcher.go	96.22% <ø> (ø)
ledger/tracker.go	74.04% <0.00%> (-3.83%)	⬇️
ledger/blockqueue.go	85.63% <0.00%> (-2.88%)	⬇️
agreement/cryptoVerifier.go	67.60% <0.00%> (-2.12%)	⬇️
agreement/proposalManager.go	96.07% <0.00%> (-1.97%)	⬇️
catchup/peerSelector.go	98.95% <0.00%> (-1.05%)	⬇️
network/wsNetwork.go	64.63% <0.00%> (ø)
cmd/algoh/blockWatcher.go	80.95% <0.00%> (+3.17%)	⬆️
network/wsPeer.go	70.88% <0.00%> (+4.85%)	⬆️

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