Renames contenderID into componentId

We introduced contenderID in a lot of places with FLINK-26522. The original multi-component leader election classes of FLINK-24038 used componentId.

Revisiting that naming made me realize that it's actually wrong. A contender is a specific instance of a component that participates in the leader election. A component, in this sense, is the more abstract concept. contenderID refers to an ID for the specific contender instance but the IDs we're sharing are actually referring to a Flink component and therefore, are the same between different contenders which compete for leadership for the same component. This contradicts the definition of an identifier.