#6151 #6212: Modifies existing Prometheus Receiver Tests to use pdata…

… directly for validations and accept staleness markers (#6219)

* Modifies existing Prometheus Receiver Tests to use pdata directly for validation

* Removed dead code from helper file

* Fixed the lint issue

* Fixing the imports lint error

* Skipping start_timestamp check for histogram and summary in target1scrape2

* Resolved feedback

* Resolved review feedback comments

* Trimming the assert messages

* Fix to avoid panic situation in assertMetricPresent method

* Moved testing as first argument in doCompare method

* Removed bool propogation in comparators and changed setupMockPrometheus to avoid replaceall on config