fix(prometheus): disable features when prometheus plugin is turned off #2248

Job	Run time
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[a-k]*)	31m 39s
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[l-z]*)	32m 28s
run ci on redhat ubi (lua-resty-worker-events, t/admin t/cli t/config-center-yaml t/control t/cor...	24m 9s
run ci on redhat ubi (lua-resty-worker-events, t/node t/pubsub t/router t/script t/secret t/strea...	21m 48s
run ci on redhat ubi (lua-resty-events, t/plugin/[a-k]*)	32m 53s
run ci on redhat ubi (lua-resty-events, t/plugin/[l-z]*)	31m 44s
run ci on redhat ubi (lua-resty-events, t/admin t/cli t/config-center-yaml t/control t/core t/deb...	24m 24s
run ci on redhat ubi (lua-resty-events, t/node t/pubsub t/router t/script t/secret t/stream-node ...	22m 30s
	3h 41m 35s

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