feat: Add support for increasing partitions to the kafka shim

[palmere-google]

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Fixes #<issue_number_goes_here> ☕️

[codecov]

Codecov Report

Merging #37 (ae0ab9f) into master (0958a5b) will increase coverage by 2.20%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master      #37      +/-   ##
============================================
+ Coverage     68.61%   70.81%   +2.20%     
- Complexity      119      127       +8     
============================================
  Files            10       10              
  Lines           564      586      +22     
  Branches         22       22              
============================================
+ Hits            387      415      +28     
+ Misses          168      161       -7     
- Partials          9       10       +1     

Impacted Files	Coverage Δ	Complexity Δ
...oogle/cloud/pubsublite/kafka/ConsumerSettings.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...oogle/cloud/pubsublite/kafka/ProducerSettings.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...gle/cloud/pubsublite/kafka/PubsubLiteConsumer.java	76.12% <66.66%> (+3.64%)	57.00 <0.00> (+4.00)
...gle/cloud/pubsublite/kafka/PubsubLiteProducer.java	80.88% <75.00%> (+1.51%)	17.00 <3.00> (+1.00)
.../google/cloud/pubsublite/kafka/SharedBehavior.java	100.00% <100.00%> (+22.22%)	5.00 <4.00> (+2.00)
...le/cloud/pubsublite/kafka/KafkaExceptionUtils.java	29.62% <0.00%> (+11.11%)	2.00% <0.00%> (+1.00%)

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