Tracking deriver invalidation issues

Monitoring integration from #3157101: Add monitoring sensor for SendGrid relies on Monitoring plugin invalidation.

#3001284: Allow plugin derivers to specify cache tags for their definitions exists to properly add tags to derivers.

#3157136: Add cache tag to KeyPluginManager exists to properly add a cache tag when Key plugins change. SendGridApiCacheTagInvalidator is only required until we can rely on #3001284: Allow plugin derivers to specify cache tags for their definitions.

Until either is committed, sensor plugins wont show associated SendGrid keys until caches are cleared.