Expose query_offest

[Gsantomaggio]

closes: #67

query the consumer offset position with: await system.QueryOffset(consumerName, stream)

example:

 const string consumerName = "myConsumer";
 var consumer = await system.CreateConsumer(
 new ConsumerConfig
 {
    Reference = consumerName,
    Stream = stream,
    OffsetSpec = new OffsetTypeOffset(await system.QueryOffset(consumerName, stream)),
           

[codecov-commenter]

Codecov Report

Merging #68 (3fbd7d5) into main (4eaf19d) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
+ Coverage   90.69%   90.80%   +0.10%     
==========================================
  Files          65       65              
  Lines        4333     4373      +40     
  Branches      257      258       +1     
==========================================
+ Hits         3930     3971      +41     
+ Misses        345      344       -1     
  Partials       58       58              

Impacted Files	Coverage Δ
RabbitMQ.Stream.Client/StreamSystem.cs	90.38% <100.00%> (+0.48%)	⬆️
Tests/ConsumerSystemTests.cs	100.00% <100.00%> (ø)
RabbitMQ.Stream.Client/QueryOffsetResponse.cs	85.00% <0.00%> (+5.00%)	⬆️

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