Add Jmeter Prometheus plugin

[GiovanniPaoloGibilisco]

Add Jmeter prometheus plugin as suggested here: johrstrom/jmeter-prometheus-plugin#82

I've removed markerClass and componentClasses from the same as I'm not sure what they should refer to.

[undera]

It's almost good. Please provide in vendor whatever name you like - it may be your company name, or your full name, or your nickname.
Also, you have to provide markerClass - it's a full Java class name of your main component, used to identify presence of plugin in Java classpath. In your plugin, com.github.johrstrom.collector.SuccessRatioCollector seem to be a valid option.

[undera]

componentClasses list all of test elements in your plugin. This field is used for nice feature when user opens JMX file on a machine without your plugin, and plugin manager offers to install missing plugin. This field is optional, you can omit it.

[GiovanniPaoloGibilisco]

I've added the vendor, marker and component classes

[codecov]

Codecov Report

Merging #408 into master will decrease coverage by 0.00%.
The diff coverage is 55.55%.

@@             Coverage Diff              @@
##             master     #408      +/-   ##
============================================
- Coverage     69.37%   69.36%   -0.01%     
- Complexity     2571     2574       +3     
============================================
  Files           230      230              
  Lines         15462    15471       +9     
  Branches       1569     1571       +2     
============================================
+ Hits          10726    10732       +6     
+ Misses         3967     3951      -16     
- Partials        769      788      +19     

Impacted Files	Coverage Δ	Complexity Δ
...md/src/main/java/kg/apc/cmdtools/ReporterTool.java	24.61% <25.00%> (-1.58%)	13.00 <0.00> (ø)
.../src/main/java/kg/apc/jmeter/PluginsCMDWorker.java	55.50% <80.00%> (+0.57%)	39.00 <1.00> (+2.00)
...ain/java/kg/apc/jmeter/jmxmon/JMXMonCollector.java	72.38% <0.00%> (+2.23%)	21.00% <0.00%> (+1.00%)

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[undera]

Looks good now. I'm merging it.
When you have new releases of your plugin, please consider creating another PR, adding new version to versions section.
Thanks for contributing!