Add Openmetric reporting for MI dataservices

[chanikag]

This is to fix #3134

To run,
On Windows: micro-integrator.bat -DenablePrometheusApi
For Linux/MacOS/CentOS : ./micro-integrator.sh -DenablePrometheusApi

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[tishan89]

This is not thread safe. If this is being used by multiple places, then you need to handle it

[chanikag]

@tishan89, this is called at the server startup by the axis2 handler and the synapse handler. Won't be called by multiple threads at the same time. Further, that won;t modify anything.

[senthuran16]

Shall we add a log here, something like: "Loading the default PrometheusReporter class"