docs: minor changes renaming pmdaprometheus to pmdaopenmetrics.
docs: minor changes renaming pmdaprometheus to pmdaopenmetrics.

modified:   man/man3/pmwebapi.3

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp