docs(serialization): add docs for protobuf-serliazation module, and send serializing

[cottand]

No description provided.

[cottand]

PR is bigger than initially planned but

• write docs for serialization module
• write docs for pollWithFlow serializing variant
• write a serializing variant of send
  • unit test
• write docs for serializing variant of send

[codecov]

Codecov Report

Merging #14 (0e73183) into master (322fd58) will increase coverage by 6.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   87.50%   93.67%   +6.17%     
==========================================
  Files           6        8       +2     
  Lines          40       79      +39     
  Branches        9       12       +3     
==========================================
+ Hits           35       74      +39     
  Partials        5        5              

Impacted Files	Coverage Δ
...ain/kotlin/io/github/kkafka/serialization/proto.kt	100.00% <ø> (ø)
...n/kotlin/io/github/kkafka/consumer/flowProtobuf.kt	100.00% <100.00%> (ø)
...n/kotlin/io/github/kkafka/producer/sendProtobuf.kt	100.00% <100.00%> (ø)
...in/kotlin/io/github/kkafka/producer/transaction.kt	100.00% <0.00%> (ø)

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