[rust] implement pushconsumer

[glcrazier]

Which Issue(s) This PR Fixes

Fixes #683

Brief Description

This is an implementation of standard and fifo PushConsumer which can consumes messages with listener provided.

How Did You Test This Change?

Sufficient unit test cases are provided and integration tests are executed.

[lizhanhui]

Thanks @glcrazier for your nice work and I would join you and review this promising feature ASAP.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.51208% with 271 lines in your changes missing coverage. Please review.

Project coverage is 83.37%. Comparing base (c8a685d) to head (2412a78).
Report is 6 commits behind head on master.

Files	Patch %	Lines
rust/src/push_consumer.rs	90.68%	72 Missing and 72 partials ⚠️
rust/src/client.rs	76.35%	58 Missing and 12 partials ⚠️
rust/src/session.rs	71.73%	26 Missing ⚠️
rust/src/conf.rs	92.43%	14 Missing and 4 partials ⚠️
rust/src/producer.rs	81.25%	2 Missing and 4 partials ⚠️
rust/src/util.rs	97.14%	1 Missing and 2 partials ⚠️
rust/src/model/message.rs	71.42%	0 Missing and 2 partials ⚠️
rust/src/model/common.rs	97.22%	1 Missing ⚠️
rust/src/simple_consumer.rs	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master     #767       +/-   ##
=============================================
+ Coverage     47.43%   83.37%   +35.93%     
=============================================
  Files           207       13      -194     
  Lines         12384     5406     -6978     
  Branches       3736     5406     +1670     
=============================================
- Hits           5874     4507     -1367     
+ Misses         6221      698     -5523     
+ Partials        289      201       -88     

Flag	Coverage Δ
cpp	?
golang	?
java	?
rust	83.37% <88.51%> (+3.54%)	⬆️

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[lizhanhui]

MSRV set to 1.61 does not make sense
run cargo msrv, we are having

[ShadowySpirits]

Rust version defined in Cargo.toml should be also bumped up to 1.70.0