fix(prometheus): disable features when plugin is turned off #2176

Job	Run time
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[a-k]*)	31m 57s
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[l-z]*)	33m 14s
run ci on redhat ubi (lua-resty-worker-events, t/admin t/cli t/config-center-yaml t/control t/cor...	25m 12s
run ci on redhat ubi (lua-resty-worker-events, t/node t/pubsub t/router t/script t/secret t/strea...	21m 41s
run ci on redhat ubi (lua-resty-events, t/plugin/[a-k]*)	32m 30s
run ci on redhat ubi (lua-resty-events, t/plugin/[l-z]*)	33m 1s
run ci on redhat ubi (lua-resty-events, t/admin t/cli t/config-center-yaml t/control t/core t/deb...	25m 4s
run ci on redhat ubi (lua-resty-events, t/node t/pubsub t/router t/script t/secret t/stream-node ...	22m 39s
	3h 45m 18s

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