libpcp_web: merge updated query grammar, add rate() actions
libpcp_web: merge updated query grammar, add rate() actions

Added rate() grammar actions for sid_vec and func_sid, to check we
can parse 'rate(somemetric)' without {qualifiers} or [time window].
Functions other than rate() still return PM_ERR_NYI.

Related https://github.com/performancecopilot/pcp/issues/1050

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