Downgrade plugin discovery camelCase warning in production

[tylersmalley]

The following continues to come up and causes confusion with users. We should either resolve these warnings in #76405 and #59191 or downgrade this warning so it's not present in production.

{"type":"log","@timestamp":"2020-08-26T16:51:13Z","tags":["warning","plugins-discovery"],"pid":14686,"message":"Expect plugin \"id\" in camelCase, but found: beats_management"}
{"type":"log","@timestamp":"2020-08-26T16:51:13Z","tags":["warning","plugins-discovery"],"pid":14686,"message":"Expect plugin \"id\" in camelCase, but found: triggers_actions_ui"}

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)