Add minimum synced ticket in PushPull response

[hackerwins]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind api-change
/kind bug
/kind cleanup
/kind deprecation
/kind design
/kind documentation
/kind failing-test

/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #3

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

[codecov]

Codecov Report

Merging #57 into master will decrease coverage by 0.46%.
The diff coverage is 39.02%.

@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
- Coverage   55.71%   55.25%   -0.47%     
==========================================
  Files          23       23              
  Lines        2554     2579      +25     
==========================================
+ Hits         1423     1425       +2     
- Misses       1038     1058      +20     
- Partials       93       96       +3     

Impacted Files	Coverage Δ
pkg/document/json/rht_pq_map.go	52.17% <0.00%> (-1.16%)	⬇️
pkg/document/json/root.go	15.51% <8.33%> (-3.54%)	⬇️
pkg/document/document.go	43.67% <66.66%> (+0.82%)	⬆️
api/converter/from_pb.go	81.38% <100.00%> (+0.09%)	⬆️
api/converter/to_pb.go	81.17% <100.00%> (+0.11%)	⬆️
pkg/document/internal_document.go	22.78% <100.00%> (+2.00%)	⬆️
pkg/llrb/llrb.go	73.46% <0.00%> (-3.41%)	⬇️

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