feat: add ChainProposedLength into the manifest

[Kubuxu]

Resolves #772

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 69.48%. Comparing base (be650d0) to head (b93a282).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
manifest/manifest.go	0.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #788      +/-   ##
==========================================
- Coverage   69.55%   69.48%   -0.08%     
==========================================
  Files          77       77              
  Lines        7896     7900       +4     
==========================================
- Hits         5492     5489       -3     
- Misses       1954     1959       +5     
- Partials      450      452       +2     

Files with missing lines	Coverage Δ
consensus_inputs.go	61.45% <100.00%> (-1.47%)	⬇️
gpbft/chain.go	87.87% <ø> (ø)
manifest/manifest.go	54.19% <0.00%> (-1.07%)	⬇️

... and 1 file with indirect coverage changes

[masih]

We might as well increment the manifest protocol version. BUT later once other changes have also landed in manifest.

[masih]

Merging this as the manifest changes I am working on would make merge tricky later.