Specify default value for tendermint::block::Size

[romac]

Close: #930

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #931 (d4d866c) into master (1a7c160) will increase coverage by 0.0%.
The diff coverage is 83.3%.

❗ Current head d4d866c differs from pull request most recent head 08d7c95. Consider uploading reports for the commit 08d7c95 to get more accurate results

@@          Coverage Diff           @@
##           master    #931   +/-   ##
======================================
  Coverage    70.5%   70.6%           
======================================
  Files         203     203           
  Lines       16264   16249   -15     
======================================
+ Hits        11475   11478    +3     
+ Misses       4789    4771   -18     

Impacted Files	Coverage Δ
tendermint/src/block/size.rs	33.3% <75.0%> (+20.8%)	⬆️
rpc/tests/kvstore_fixtures.rs	95.5% <100.0%> (+<0.1%)	⬆️
tendermint/src/signature.rs	58.9% <0.0%> (-1.7%)	⬇️
tendermint/src/channel.rs	37.4% <0.0%> (-0.9%)	⬇️
tendermint/src/consensus/params.rs	4.2% <0.0%> (-0.6%)	⬇️
light-client/src/types.rs	30.1% <0.0%> (-0.3%)	⬇️
tendermint/src/node.rs	65.7% <0.0%> (-0.3%)	⬇️
tendermint/src/abci/path.rs	0.0% <0.0%> (ø)
tendermint/src/channel/id.rs	25.0% <0.0%> (ø)
tendermint/src/config.rs	64.5% <0.0%> (+0.2%)	⬆️
... and 3 more

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